Historical Evolution and Current Developments in Building Thermal Insulation Materials—A Review

Abstract

The European Climate Law mandates a 55% reduction in CO₂ emissions by 2030, intending to achieve climate neutrality by 2050. To meet these targets, there is a strong focus on reducing energy consumption in buildings, particularly for heating and cooling, which are the primary drivers of energy use and greenhouse gas emissions. As a result, the demand for energy-efficient and sustainable buildings is increasing, and thermal insulation plays a crucial role in minimizing energy consumption for both winter heating and summer cooling. This review explores the historical development of thermal insulation materials, beginning with natural options such as straw, wool, and clay, progressing to materials like cork, asbestos, and mineral wool, and culminating in synthetic insulators such as fiberglass and polystyrene. The review also examines innovative materials like polyurethane foam, vacuum insulation panels, and cement foams enhanced with phase change materials. Additionally, it highlights the renewed interest in environmentally friendly materials like cellulose, hemp, and sheep wool. The current challenges in developing sustainable, high-performance building solutions are discussed, including the implementation of the 6R principles for insulating materials. Finally, the review not only traces the historical evolution of insulation materials but also provides various classifications and summarizes emerging aspects in the field.

1. Introduction

Thermal insulation refers to materials that minimize heat transfer between areas with differing temperatures. By creating a barrier that slows down conductive, convective, and radiative heat transfer [1,2,3,4], thermal insulation effectively reduces both heat loss and gain. Simultaneously, it should be mentioned that thermal insulation materials can effectively slow down convective heat transfer, but the extent of this depends on the specific conditions. Convective heat transfer occurs when heat is transferred through the movement of fluids, such as air or a liquid, and insulation materials limit this by trapping air or other gases in small pockets, thereby reducing their movement. One key condition is the presence of air trapped in small spaces. Many insulation materials, like fiberglass, foam, or mineral wool, are designed to contain numerous small air pockets. Since air has low thermal conductivity, its movement is restricted in these spaces, minimizing convective heat transfer. The smaller the air pockets, the better the insulation. Another important condition is a closed system, such as between walls, where insulation materials trap air and prevent it from circulating freely. This containment reduces convection, helping maintain a stable internal temperature. The temperature gradient between the inside and outside of a building also affects insulation performance. A larger temperature difference may induce stronger convection effects, but high-quality insulation can still restrict air movement and limit heat transfer. However, if the insulation is poorly installed or allows air to circulate freely, convection will not be effectively slowed, reducing its insulating capacity. Therefore, properly installed insulation materials work by trapping air and preventing fluid movement, slowing conductive and convective heat transfer, thus improving energy efficiency. All these issues are crucial for keeping comfortable indoor temperatures, enhancing energy efficiency, and decreasing the energy needed for heating and cooling—not only in buildings but also in industrial systems. The effectiveness of thermal insulation is largely due to the materials’ low thermal conductivity, which allows them to resist heat flow effectively. At its core, thermal insulation seeks to minimize heat transfer between two areas with differing temperatures. Its effectiveness hinges on reducing thermal conductivity, thus preventing heat loss in colder climates or inhibiting heat gain in warmer ones. Over the centuries, a diverse array of materials have been employed to achieve these goals, each with unique properties and limitations. While early insulation methods focused primarily on comfort, contemporary techniques prioritize energy conservation, greenhouse gas emission reduction, and sustainable building practices.

Thermal insulation is a key factor in enhancing building energy efficiency, directly influencing the energy demands of heating, ventilation, and air conditioning systems. In this case, air permeability is a key factor, as low-permeability insulation minimizes air leakage, helping to maintain stable indoor temperatures. However, insufficient air exchange can trap pollutants, making proper ventilation essential to ensure fresh air circulation without compromising thermal efficiency. Moisture resistance and vapor permeability are equally important. Insulation that resists moisture buildup helps prevent condensation and mold, protecting the air quality. Materials with good vapor permeability, such as mineral wool, allow moisture to escape, reducing the risk of dampness and structural damage. When combined with adequate ventilation, such materials ensure a balanced indoor environment, controlling humidity while maintaining thermal performance. Furthermore, from an environmental and health perspective, some traditional insulation materials can off-gas harmful chemicals like volatile organic compounds (VOCs). This requires effective ventilation to maintain indoor air quality. Selecting eco-friendly, non-toxic insulation materials minimizes the reliance on mechanical ventilation for air purification, creating healthier indoor spaces. Proper coordination between insulation and ventilation systems is essential to achieving energy efficiency while safeguarding occupant health and comfort.

According to the International Energy Agency (IEA), buildings account for about 40% of global energy consumption, with a significant portion distributed to space heating and cooling [5,6]. Improvements in insulation materials and techniques thus hold great potential for reducing the global energy demand, especially in regions with extreme weather conditions. The significance of thermal insulation extends beyond residential and commercial buildings; it is also vital in industrial processes, refrigeration, and the transportation sector.

For millennia, thermal insulation has played a pivotal role in building design and construction, helping to regulate indoor climates and reduce energy consumption. As global awareness of energy efficiency and sustainability has increased, the evolution of insulation materials and technologies has accelerated. This shift aligns with the growing demands of building occupants for better indoor comfort, reduced energy costs, and reduced environmental impact. Occupants now more often prioritize sustainable solutions that enhance thermal performance while also contributing to healthier living environments. Additionally, this shift is further propelled by regulations such as the European Climate Law, which mandates a 55% reduction in greenhouse gas emissions by 2030, with a target of climate neutrality by 2050 [7,8,9]. To meet these ambitious goals, significant efforts are being directed toward reducing energy usage in buildings, especially since heating and cooling represent major sources of energy consumption and emissions. Consequently, there is a growing demand for energy-efficient and sustainable buildings, with thermal insulation being integral to lowering energy requirements during both winter and summer.

The history of insulation mirrors broader technological advancements, ranging from rudimentary natural materials used in ancient structures to today’s sophisticated, high-performance insulation solutions [10,11,12,13,14]. This progression has been influenced not only by innovations in materials science but also by societal demands, energy crises, environmental regulations, and an increasing recognition of climate change’s impacts. A crucial aspect of developing sustainable building practices involves managing insulation materials at the end of their life cycle. This challenge aligns with ongoing standardization efforts and regulations within the European Union, particularly the implementation of Environmental Product Declarations (EPDs). The EPD standard was updated in 2022 to EN 15804+A2 [15] to require the inclusion of end-of-life impact calculations and expand the scope to consider benefits beyond the system boundary, such as the reuse, recovery, and recycling of materials. Although the EPD publication remains voluntary, many insulation manufacturers are already releasing EPDs to prove the sustainability of their products. The forthcoming EU Construction Products Regulation is expected to make EPDs mandatory, requiring recyclability assessments for all construction materials, including insulation. This shift is vital, particularly for materials that are petroleum-based or contain chemicals that complicate disposal. By ensuring that insulation materials can be recycled or reused, the construction industry can significantly decrease landfill waste and mitigate the environmental impacts of raw material extraction. Recycling insulation materials—whether natural, synthetic, or hybrid—will contribute to a circular economy in the sector, fostering sustainable building practices and resource conservation.

For insulation materials to be effective, they must maintain reliable performance throughout a building’s life cycle [16,17,18]. However, thermal efficiency alone is insufficient when selecting insulation. The building sector is increasingly adopting a holistic approach to material selection, taking into account factors such as sound insulation, fire resistance, water vapor permeability, and the environmental impact of the materials, including their effects on human health. This comprehensive perspective fosters more sustainable and well-rounded building solutions.

This review aims to explore the historical evolution of thermal insulation materials, highlighting key developments and innovations that have shaped the field. By examining the various types of materials used throughout history—from natural fibers and mineral-based insulators to advanced synthetic materials and nanotechnology—we can gain a deeper understanding of the technological advancements that have improved insulation performance over time. Furthermore, this review will assess the current trends in thermal insulation, such as the increasing emphasis on sustainability, the development of eco-friendly materials, and the integration of cutting-edge technologies to enhance energy efficiency. It will cover insulation performance metrics, energy efficiency contributions, and key challenges facing the industry, underscoring the ongoing need for sustainable, high-performance solutions in building design. Finally, alongside exploring the historical development of insulation materials, this article presents various classifications and shows emerging aspects and their advancement.

2. Evolution of Thermal Insulation Materials

2.1. Early Insulation Materials

The use of thermal insulation materials in prehistorical and preindustrial times reflects humanity’s ongoing effort to adapt to environmental conditions, particularly temperature extremes. Early humans faced the challenge of surviving in harsh climates, which led them to develop methods and materials to insulate their dwellings from both cold and heat. These methods relied heavily on natural, locally available materials, such as straw, mud, and wool, which provided basic yet effective insulation against heat loss. For example, the ancient Egyptians utilized mud bricks mixed with straw to insulate their homes, while the Romans employed cork and wool in their construction projects [10,11,19,20,21]. Despite their simplicity, these techniques maintained indoor comfort in extreme climates.

Throughout history, building materials themselves often functioned as insulators. In particular, materials with a high thermal mass, such as stone, wood, and various earth-based materials, played a key role in stabilizing indoor temperatures by absorbing and releasing heat [22,23]. Earth-sheltered houses and cave dwellings were especially popular for their natural thermal properties [24,25,26]. One notable example is the Neolithic Skara Brae settlement (3180–2500 BC) on the Orkney Archipelago of Northern Scotland where earth-covered houses offered excellent insulation [27,28,29]. Similar constructions were found across the Nordic regions, from Greenland to Russia and Alaska. Indigenous cultures worldwide, including the Maya, Inca, and Aztecs, built homes using natural materials like grass and straw, underscoring the global importance of insulation [30,31].

Even in prehistoric times, humans recognized the need for thermal protection. Animal skins and wool were commonly used for personal insulation, while natural caves and shelters provided refuge from the elements [32,33,34]. Region-specific materials were often employed, with leaves, reeds, and grass used in tropical climates, and snow or ice blocks utilized in far northern regions. These early methods of insulation show a deep understanding of local environments and a global approach to managing thermal conditions.

In historical architecture, the insulative function was often inherent in the building materials themselves, which also acted as heat storage. Building materials like thick stone or brick walls provided both insulation and thermal mass, allowing them to store heat. These materials had a high density, enabling them to absorb and slowly release heat, which helped regulate indoor temperatures. In contrast, modern insulation materials typically have a low density, which affects their ability to store energy. Insulation materials like fiberglass, foam, or mineral wool are designed primarily to minimize heat transfer through conduction, convection, and radiation, but they are not intended to store energy. Their low density limits their thermal mass, meaning they do not absorb and retain heat the way traditional, denser materials do. Instead, they excel at creating a barrier that prevents heat from entering or leaving a space. Therefore, materials with a high thermal capacity contributed to the thermal stability of rooms by absorbing heat during the day and releasing it at night. In wooden architecture, layered walls were constructed by combining wood with natural materials such as clay or straw, and the log structures were sealed with woven straw to enhance insulation [35]. Corner joints in wooden buildings were carefully constructed to prevent heat loss by extending wooden beams beyond the bond, creating “ends” that lengthened the path for cold air, protecting the structure from freezing. Churches built with these techniques provided excellent protection against cold, heat, and precipitation while maintaining significant durability [36,37].

Later, in brick architecture, builders sought to improve insulation by creating layered walls and incorporating buffering spaces within walls and roof finials. Since Roman times, walls were often constructed with stone or brick exteriors, filled with rubble and lime mortar, which created a porous internal structure that enhanced thermal insulation [38]. This method was also applied to domes, where structural layers were sometimes separated by air gaps. Additionally, parts of buildings were often placed below ground level to protect them from external temperature extremes, and multi-story systems were employed to further enhance insulation.

In the Middle Ages, construction techniques evolved to reflect a broader philosophical understanding of space [39,40]. For example, windows and doors were often avoided on the northern side of buildings, which was considered a zone of evil and cold. Instead, sacristies or annexes were built to act as buffer zones, protecting the main structure from the elements. Wooden churches from the Middle Ages to the 19th century maintained functional layouts that aligned with the principles of sustainable construction, where windows were primarily positioned on the southern and eastern sides for optimal lighting and heat retention.

An important aspect of historical architecture was heat storage, where materials with a high heat capacity acted as thermal reservoirs. The heat from the sun, heating systems, and even occupants was absorbed and gradually released, maintaining energy stability within buildings. This principle of heat storage was also used in heating systems that were advanced for their time. A notable example is the central heating system built before 1340 in Malbork Castle in Poland, which used large river stones to store heat [41]. The system employed a dual-circuit design—one for clean air and another for exhaust gases—which provided high comfort levels by circulating warm, clean air through the building after heating the stones.

In the 19th century, the concept of heat storage continued to influence the development of ventilation systems. Innovations such as “roof ventilation” systems, where supply air was preheated through double walls, laid the groundwork for modern heat recovery systems. These systems, which allowed the exchange of heat between incoming and outgoing air, marked a significant step forward in energy-efficient building design and are still relevant today in sustainable architecture [40].

Therefore, the distinction between thermal mass (heat storage) and insulation (heat transfer reduction) should be underlined. Modern low-density insulation focuses on reducing heat flow rather than storing it. Thus, while they efficiently keep buildings warm or cool by limiting heat exchange, they do not contribute to heat storage like the dense materials used in historical architecture do. The evolution of building design has shifted toward separating these two functions—insulation for reducing heat flow and materials with a high thermal mass for energy storage; however, both may work together for optimal energy efficiency [42]. Thus, the history of thermal insulation materials is deeply intertwined with the development of human civilization, showcasing the continuous innovation and adaptation of building techniques to create more comfortable, energy-efficient, and sustainable living environments.

2.2. Nineteenth and Early Twentieth Century: Industrial Revolution

The Industrial Revolution, which began in England between 1840 and 1920, was driven by groundbreaking technological innovations and later spread across the European continent and served as a major catalyst for advancements in construction and material technologies. The industrial production of iron and glass, along with the widespread use of reinforced concrete, played a crucial role in revolutionizing construction and architectural design [11,43,44]. While these new materials enabled greater freedom in architectural forms, they also introduced the challenge of developing more effective thermal insulation systems, as the high thermal expansion and permeability of these materials increased the risk of structural damage due to stresses, cracks, and heat loss. Simultaneously, the rapid urbanization and industrialization of cities, driven by mass migration to industrial jobs, spurred the rapid expansion of housing infrastructure. The new housing estates and workers’ districts needed to be built quickly and at minimal cost, which required the development of optimal solutions in building materials, construction technologies, and architectural design.

2.2.1. Cork

Initially, natural materials that had been known for centuries were employed, though not on such a large scale due to earlier technological and economic constraints. During this period, cork—the bark of the cork oak (Quercus suber L.)—became particularly popular, especially in the Mediterranean region where it had been valued as an excellent insulating material since ancient times [45]. Archaeological evidence shows that cork was used in ancient Egypt around 3000 BC [10,11]. Its first documented mention appears in Pliny the Elder’s Natural History (1st century AD), where he describes its use in construction, including for roofing. In the Middle Ages, cork was widely used in rural buildings across Portugal, Spain, and North Africa, where cork trees are native. It was applied to roofs and walls, often mixed with earth or lime. To enhance thermal comfort, cork sheets were also used as interior cladding for walls and ceilings, and around windows and doors [46,47].

While this section covers the Industrial Revolution and the technological innovations that emerged during this period, it is also important to highlight the historical continuity of the materials used. Cork has been known for centuries, but it was only with advancements in science and technology that its unique properties as a natural insulating material were fully understood. Additionally, technological developments enabled the processing of cork, the creation of new materials, and its application in innovative ways, such as multilayer boards made from expanded cork and building blocks from forest cork waste for quick and easy assembly. To illustrate the evolution of this material, it was necessary to reference its historical use in antiquity and the Middle Ages.

The exceptional properties of cork—such as its low thermal conductivity, hydrophobicity, and elasticity—were fully recognized during the Industrial Revolution. Its popularity spread globally, driven by international trade and the mass cultivation of cork oaks for bottle cork production [48,49,50]. The industrial process generated significant cork waste, which, through advancements in technology, was repurposed into insulation materials for construction. By the mid-19th century, new inventions enabled the bonding of cork granules with various binders, leading to the production of cork boards, bricks, and mats. In 1855, Frederic Walton invented cork linoleum, a product made from canvas coated with a mixture of cork flour, minerals, and linseed oil. A breakthrough occurred in the late 19th century with the development of the expansion process, which allowed cork granules to be fused without additional binders by heating them to release natural resins. This process led to the creation of expanded cork products that were used in a wide range of applications, from cold storage and refrigeration to building materials for thermal and acoustic insulation [51].

Prominent modernist architects such as Le Corbusier, Walter Gropius, and Frank Lloyd Wright also embraced cork for its physical and aesthetic qualities [51]. However, by the mid-20th century, the market share for cork insulation declined due to the emergence of cheaper synthetic materials, such as polyurethane foam and polystyrene, which offered similar insulating properties at lower production costs. Today, with the increasing global emphasis on sustainability and ecological construction, there is a renewed interest in natural materials like cork. Its biodegradability and low environmental impact appeal to architects and investors looking to minimize carbon footprints and promote healthier indoor environments. Technological innovations have further improved the efficiency of cork processing, making it an increasingly attractive choice for sustainable construction projects.

It is worth mentioning that the periodic renovation of cork trees is a prime example of a sustainable forestry practice that aligns with ecological and environmental principles. Unlike most trees, cork oak trees are not cut down during harvesting. Instead, their bark is carefully removed in cycles every 9 to 12 years, allowing the tree to regenerate naturally. This process not only ensures the continuous production of cork, a biodegradable and renewable resource, but also promotes the long-term health and stability of cork oak forests [51]. These forests, predominantly found in the Mediterranean region, provide vital ecosystems for biodiversity, act as significant carbon sinks, and prevent soil erosion. The periodic renovation and careful stewardship of cork trees demonstrate a balance between economic gain and environmental preservation, making it a highly sustainable practice in the context of green building materials and responsible land management.

2.2.2. Insulation Materials from Wood Waste: Shavings, Sawdust, and Wood Pulp

During the Industrial Revolution, a similar process was applied to waste from the wood industry. Due to its wide availability and low cost, wood waste became a popular choice for insulation materials [52,53,54,55,56]. By-products such as wood shavings, sawdust, and wood pulp, often sourced from the paper industry, were used to produce insulating boards around the turn of the 19th and 20th centuries. These materials were employed for wall and roof insulation as well as interior finishing. The first plant to manufacture insulating fiberboards was established in 1898 in Sunbury-on-Thames, England [11]. In continental Europe, similar plants appeared about 10 years later, such as in Ferndorf, Austria, in 1908, and in North America in 1914 in Minnesota [10]. Advances in production technology improved the panels’ resistance to moisture, mold, and fire. To enhance fire resistance, the boards were coated with asbestos cement on one or both sides, making them widely used in residential construction [57].

In the 1920s, wood industry waste mixed with wastepaper was used as loose-fill insulation for walls and floors, placed between the layers of wooden structures. This method gained popularity in Scandinavia and later spread to Germany, where the first production plant and specialized equipment for installing this type of insulation were established in 1928 [10,57].

Another category of insulating materials consisted of boards made from wood waste and sawdust bound with mineral binders. The development of these materials was made possible by Stanislas Sorel’s 1867 discovery of a binder made from caustic magnesite and magnesium chloride, which was used to produce wood wool boards and sawdust insulation [11,57]. In Central and Eastern Europe, cement-chip boards and blocks, made from a combination of coniferous wood chips, cement, lime, and minerals, became widespread from the 1940s onward [58,59,60]. A notable product, known as Suprema, was developed in the 1930s by Zdzisław Krudzielski’s team at the Szczakowa Cement Factory in Poland. It was designed as a relatively inexpensive material for partition walls and building insulation, which was made entirely from production waste such as ground, improperly burned cement clinker and chips and sawdust from cement barrels.

2.2.3. Wood Wool

Wood wool has a long history of use as an insulating material [61,62]. It is made from thin, long strands of wood that are curled and interwoven to form a fibrous, lightweight material [63,64,65,66]. The use of wood wool in construction and insulation has evolved over the centuries, influenced by advances in industrial processes and the need for cost-effective, sustainable materials. Wood wool was originally used for packaging and cushioning delicate items during shipping. Its lightweight and fibrous nature made it ideal for protecting goods, especially during the 19th century industrial era when transportation of fragile items became more common. However, the qualities that made wood wool effective in packaging—its thermal insulating properties, low weight, and affordability—soon led to its application in building construction.

The history of wood wool insulation dates to 1842, when Mr. von Pannewich from Wrocław, Poland, began producing bedspreads by processing pine needles [11,57]. The introduction of the first shredding machines in 1876 enabled the mass production of wood wool. Due to its hygroscopic properties, wood wool was also used to make towels and diapers. Wood wool’s potential as a thermal and acoustic insulator was discovered in the early 20th century, around the time when the demand for energy-efficient and fire-resistant materials began to grow, especially with the rising costs of heating. By combining wood wool with other binders, such as cement or gypsum, manufacturers were able to create lightweight, durable panels that provided both structural support and insulation. However, it was not until the early 20th century that the idea of producing insulation panels from wood wool emerged. In 1908, the Heraklith company in Ferndorf, Austria, produced the first wood wool insulation product, using magnesite and cement as binders [61,67]. While the first products had several drawbacks, such as flammability and poor dimensional stability, wood wool insulation quickly gained popularity and spread worldwide. The real breakthrough in the use of wood wool as an insulation material came with the development of composite wood wool panels. In the 1920s and 1930s, companies began producing wood wool cement boards, where the wood fibers were mixed with cement and formed into rigid panels. These panels provided good thermal insulation, sound absorption, and fire resistance [68,69].

After World War II, the need for affordable and efficient construction materials was greater than ever, especially in war-torn regions that needed quick rebuilding. Wood wool insulation saw increased use in both Europe and North America. Its availability, low cost, and ease of installation made it a popular choice during the mid-20th century. During this time, wood wool was used not only for insulating walls and ceilings but also for insulating cold storage rooms, livestock shelters, and agricultural buildings. In recent decades, the demand for environmentally friendly, sustainable building materials has revived interest in wood wool as an insulation material [70,71]. Unlike many synthetic insulation materials, wood wool is biodegradable, renewable, and has a relatively low environmental footprint. Modern wood wool panels are often combined with other natural or recycled materials to enhance their performance while being sustainable.

2.2.4. Asbestos

Asbestos is a natural fibrous mineral that occurs in six varieties, categorized into two main groups: amphibole asbestos and serpentine asbestos [72]. The amphibole group includes crocidolite, amosite, tremolite, actinolite, and anthophyllite, while the serpentine group consists of chrysotile, which accounts for about 95% of all asbestos products [57,73,74]. Although asbestos was known in ancient times, its widespread use began during the Industrial Revolution. The earliest evidence of asbestos use, dating to around 2500 BC, comes from Finland, where it was used to seal wooden log cabins and reinforce ceramics. The ancient Greeks and Romans valued asbestos for its low thermal conductivity [75], fire resistance, and resistance to acids, employing it in the production of fabrics, armor, and unquenchable wicks for oil lamps [10,72]. The name “asbestos” is derived from the Greek word meaning “unquenchable”.

In the Middle Ages, asbestos fell into obscurity, but its modern usage was revived in the mid-19th century following the discovery of large deposits in Canada and South Africa. Initially used as an external insulating material for furnaces, asbestos quickly found applications in construction and shipbuilding due to its excellent insulating properties. It was widely used to insulate pipes, boilers, and steam engines in locomotives and engine rooms [57].

Asbestos use surged in the late 1920s and early 1930s, finding applications in specialist textiles, brake and clutch pads, household goods, and even in the pharmaceutical and food industries [72]. Due to its fire resistance and low thermal conductivity, asbestos became particularly popular in construction. It was most utilized in asbestos cement for roofing and façade panels, as well as in floor and acoustic tiles for interior use. A less common application involved its use in thermal insulation materials, such as loose-fill insulation, insulating mats, and spray-on insulation, particularly in attics of residential homes between the 1930s and 1950s [11,57,72]. Asbestos usage peaked in the 1970s, with the U.S. consuming approximately 775,000 tons annually, while Germany led Europe with 400,000 tons [72,76].

The potential health risks of asbestos were noted as early as ancient times. In the 1st century BC, the Roman historian Pliny the Younger documented the poor health of slaves working in asbestos mines. Despite these early warnings, asbestos was largely forgotten until its mass extraction and widespread use in the late 19th century, which led to the systematic documentation of its harmful effects. An 1898 report highlighted the negative impact of asbestos on workers in the British textile industry, and in 1906, British physician Hubert Murray recorded the first medically confirmed death linked to asbestos [77,78,79]. In the U.S., concerns appeared in 1918 when insurance companies refused to provide life insurance to workers involved in asbestos production.

Over the following decades, the dangers of asbestos became more apparent. Doctors found lung fibrosis caused by asbestos exposure, with the term “asbestosis” first coined by Cooke in 1924 [72]. The connection between asbestos and lung cancer was suggested in the 1930s by American doctors Lynch and Smith, and it was scientifically confirmed in the first epidemiological study in 1955. Similar reports emerged from Germany, the Netherlands, and South Africa during the 1950s, noting increased incidences of asbestos-related diseases not only among workers in asbestos mines and factories but also among residents exposed to the material.

These discoveries have led to a reduction in global asbestos extraction and stricter regulations on its use and disposal. Currently, over 50 countries have implemented restrictions on asbestos, although these regulations vary significantly. While highly developed countries [80] typically show greater awareness of asbestos’s harmful effects on human health, this awareness does not always translate into stringent legal measures. Authorities often lack coherence and consistency in their actions. The European Union enacted a complete ban on asbestos use in 2005, while a partial ban in the United States did not take effect until 2024. Despite these measures, asbestos mining continues in Russia, Kazakhstan, and China, and its use remains permissible in many so-called developing countries [77]. It should be also mentioned that due to the harmful effects of asbestos and its ban in many countries, efforts have been made to find substitute materials [80]. Other fibrous materials, both natural and synthetic, can serve as alternatives to asbestos fibers. Generally, mineral wool and ceramic fibers are recommended as the most suitable alternatives for asbestos fiber insulation. In insulation boards, asbestos can be effectively replaced with glass, cellulose, or carbon fibers. For cement boards, alternatives include cellulose fibers, polypropylene fibers, polyvinyl alcohol fibers, aramid fibers, and glass fibers. In textiles and mats that contain asbestos, polyethylene, polypropylene, polyamide, carbon, and glass fibers can be used instead. However, it is important to note that some of these fibers have also been found to be harmful or potentially harmful to health.

2.3. Mid- and Late 20th Century: Advances in Thermal Insulation Materials

The mid- and late 20th century was a period of rapid advancement in thermal insulation materials, driven by a growing awareness of energy efficiency, rising energy costs, and the need for improved building performance [57]. This period saw significant innovations, from the development of new synthetic materials to advancements in traditional insulation technologies, all aimed at enhancing thermal resistance, fire safety, durability, and environmental sustainability. The oil crises of the 1970s underscored the world economy’s heavy reliance on fossil fuels, particularly crude oil. The first crisis in 1973, triggered by an oil embargo imposed by OPEC countries, caused a sharp spike in oil prices. The second crisis in 1979 further destabilized supply chains, leading to another surge in prices. This resulted in a significant increase in energy costs across the Western world, including the energy required to maintain thermal comfort in buildings. Consequently, many countries, particularly in Europe and North America, were compelled to rethink their approach to energy efficiency in construction. Interest grew in building airtightness, heat recovery, passive technologies, and advanced insulation materials. This shift in focus also led to the widespread adoption of materials that had been previously discovered but now benefited from improved production technologies and lower costs, making them more viable as insulation materials. This development became a catalyst for the growing popularity of previously known thermal insulation materials, including, among others, mineral wool, which played a significant role in transforming the construction market.

2.3.1. Mineral Wool

In common nomenclature, the term “mineral wool” refers to a group of inorganic fibrous materials, including slag wool, rock wool, and glass wool [81,82,83,84]. These materials share similar chemical and physical properties but differ in the raw materials used for their production. Rock wool is made from natural rocks such as basalt, diabase, and dolomite, while slag wool is primarily produced from blast furnace slag, a byproduct of iron ore processing. Glass wool is manufactured by processing quartz sand and glass waste.

The history of these materials dates to 1840, when Edward Parry in Wales observed that molten slag could be formed into fibers [10,57,85]. The industrial method for producing slag wool was patented in the United States in 1870 by John Player, and commercial production began in 1871 in Georgsmarienhütte, Osnabrück, Germany. Rock wool was first produced in the United States in 1897 by chemist C.C. Hall [11,57]. However, it was not until the 1950s that slag wool and rock wool began to be produced and used on a larger scale, particularly in lightweight frame structures [86].

Glass fibers, on the other hand, were already being produced in ancient times through the drawing process in glass workshops, where they were used to decorate glass objects without any understanding of their insulating properties. In 1836, Parisian craftsman Ignace Dubus-Bonnel, inspired by the production of cotton candy, patented a loom for weaving glass fibers. Large-scale production did not begin until John Player refined the process in 1870 by blowing fibers with a jet of steam. The modern method was developed in 1932 by Dale Kleist, who used a high-pressure air stream directed at liquid glass to produce fine fibers in industrial quantities [10]. Since then, glass fibers have been used in fabrics, the automotive industry, home and sports equipment, and as thermal insulation in the form of glass wool.

During the 1920s and 1930s, the use of mineral wool expanded significantly as building codes began to emphasize the fire safety of buildings [87]. Its non-combustible nature made it a popular choice for insulating public buildings, schools, and factories. In addition, advancements in manufacturing techniques improved the quality and affordability of mineral wool, leading to wider adoption. After World War II, the demand for efficient insulation materials surged, and mineral wool became a staple in residential construction. Its versatility allowed for various applications, including soundproofing and thermal insulation in walls, roofs, and attics. Introducing new formulations and products, such as batts, boards, and loose-fill insulation, further enhanced its market presence. Throughout the late 20th century, concerns about the environmental impact and health effects associated with some insulation materials led to increased scrutiny of mineral wool. However, it was generally considered safe, especially compared to alternatives like asbestos. The development of eco-friendly manufacturing processes also helped bolster its reputation. Today, mineral wool remains a widely used thermal insulation material, favored for its fire resistance, sound absorption, and sustainability. Innovations continue to appear, including the use of recycled content and improved production methods, suggesting that mineral wool will play a vital role in energy-efficient building practices for years to come [81,88,89,90,91].

2.3.2. Fiberglass and Foam Glass

Fiberglass insulation, originally developed in the 1930s, has seen significant advancements over the years, becoming one of the most used materials in residential and commercial construction [10,92]. Made by spinning molten glass into fine fibers, fiberglass traps air, reducing heat transfer and providing an effective thermal barrier at a low cost. The material’s fire-resistant properties, ease of installation, and versatility across different formats—such as batt, loose-fill, and blown-in insulation—contributed to its widespread popularity throughout the mid-20th century. By the late 20th century, improvements in manufacturing techniques enhanced fiberglass’s energy efficiency, durability, and environmental safety, making it even more reliable for insulation. However, the roots of fiberglass stretch back much further, with the ancient Egyptians and Venetian glassmakers discovering how to make fine threads from molten glass to decorate vessels [13,14]. However, the mass production of fiberglass only became possible with the invention of fine-set machines. In 1893, Edward Drummond Libbey experimented with glass fibers as thin as silk, paving the way for the first commercial fiberglass insulation. In 1938, Russell Games Slayter, a researcher at Owens Corning, introduced fiberglass insulation as we know it today.

As environmental awareness grew in the 21st century, fiberglass insulation continued to evolve, with manufacturers reducing volatile organic compound (VOC) emissions and creating high-performance, eco-friendly versions [93]. Today, it remains a top choice for builders due to its cost-effectiveness, energy efficiency, and compliance with modern sustainability and building standards. Modern fiberglass is made from a blend of quartz sand, limestone, dolomite, and 50–60% recycled glass [94,95,96]. These fibers are coated with a binder, typically phenol–formaldehyde resin, and formed into insulating blankets that remain a staple of the insulation industry.

Foam glass, also known as cellular glass, is a lightweight, rigid, and highly durable insulating material made from recycled glass [97,98,99]. It is produced by heating crushed glass with a foaming agent, such as carbon or limestone, to create a cellular structure filled with sealed air pockets. This unique structure gives foam glass its excellent insulating properties and a range of other valuable characteristics, making it a versatile material in both construction and industrial applications. In the 1930s, three similar patents emerged for the production of foam glass. In 1931, American inventor Albert L. Kern patented a method that involved using silica mixed with 20% combustible materials, such as lignite, coal, or wood, along with foaming agents like hydrochloric acid and sodium hydroxide solution. This mixture was heated to 1500 °C, resulting in a porous material. In 1932, I. I. Kitaigorodsky, a laboratory engineer at the Mendeleev Institute in Moscow, developed a different approach. He combined finely powdered glass with calcium carbonate (CaCO₃) as the foaming agent and heated the mixture to 850 °C. Afterwards, it was cooled in steel molds to form the final product. A third method was introduced in 1934, using a combination of finely powdered silica, borax, and zinc oxide. During heating, the gases released were trapped, creating a cellular structure filled with bubbles. This process was further refined by William O. Lytle, a technician at Pittsburgh Plate Glass & Corning Glass Works in Pennsylvania, USA. In 1940, Lytle patented a technique that included additional foaming agents, such as air and water vapor, to create more pores in the material. The resulting foam glass was lightweight, rigid, and resistant to fire, water, rodents, and insects, making it an ideal insulation material [100,101,102]. Mass production of foam glass began in 1943 in Port Allegany, Pennsylvania, marking its successful introduction as a new form of insulation.

2.3.3. Plastic Foams

The scientific and technological advancements of the early 20th century, particularly in chemistry and organic chemistry, led to the discovery of several petroleum-based plastics that later became important insulating materials in construction. The process of polymerization, which underpinned these discoveries, had been known for centuries. Even in ancient times, people utilized natural polymers derived from sources like rubber trees and keratin. Polymerization as a natural process was first described in 1838 by French chemist and physicist Henri Victor Regnault [10,24,103]. By the 19th century, various polymers had been discovered, including polyvinyl chloride (1838, 1872), vulcanized rubber (1839, 1943), ebonite (1851), and celluloid (1856) [10].

The foundation for the invention of polystyrene was laid with the discovery of styrene by German pharmacist Eduard Simon in 1839. This discovery was further developed by German chemist Hermann Staudinger, who won the Nobel Prize in 1956. In 1922, Staudinger demonstrated that heating styrene could trigger a chain reaction, leading to the formation of polystyrene macromolecules. Originally, styrene was derived from the natural resin of styrax trees, but today it is synthetically produced from crude oil [103,104,105]. The first industrial-scale production of synthetic styrene monomers occurred in 1929 at BASF in Ludwigshafen, Germany, under the direction of Hermann Franz Mark, followed by Karl Eulff and Eugen Doerrer in 1930. The development of styrene-containing polymers accelerated with the large-scale processing of plastics, driven by the demands of World War II [10].

The technology for foaming polystyrene was developed in 1931 by Carl Georg Munters and John Tandberg [57]. Further refinements led to the creation of expanded polystyrene (EPS) foam in 1950 by engineers from IG Farbenindustrie AG in Germany. Industrial production of extruded polystyrene (XPS) began in 1941 at the Dow Chemical Company, with the first insulating boards, branded as Styrofoam R, hitting the market in 1943. The production of expanded polystyrene (EPS) became possible thanks to the invention of pre-foamed polystyrene granules by Czech engineer Fritz Stiasny, who was working for BASF. These granules were used to manufacture insulating boards, which were introduced in 1951 under the name Styropor R [10,11].

Polyurethanes, a group of polymers produced through the polyaddition process, were discovered in 1933 by Reginald Gibson and Eric Fawcett in England during the synthesis of polyethene. Building on this research, Otto Bayer successfully synthesized polyurethane in 1937 at the IG Farbenindustrie AG laboratory in Leverkusen, Germany. Early polyurethane production involved reactions between polyurea-generating diamines and aliphatic diisocyanate, but glycol later replaced polyurea in the process. Subsequent modifications improved the material’s properties, and polyurethanes quickly gained importance during World War II, where they were used as rubber substitutes, paper and uniform coatings, and anti-corrosion layers.

The breakthrough in polyurethane usage occurred in the 1950s with the development of flexible polyurethane foams based on toluene diisocyanate (TDI) and polyester polyols. The first rigid insulating boards appeared in 1954. In 1967, further innovation led to the introduction of rigid foams modified with urethane, offering enhanced thermal insulation and fire resistance, making them widely used as insulation materials in construction [104,106,107,108].

2.3.4. Cellulose Insulation

Cellulose insulation first appeared in the 1920s in Scandinavia, where it was produced from forestry by-products [10,11,13]. Initially, it was used as core insulation in traditional half-timbered houses and occasionally for insulating attic spaces. Today, cellulose insulation is widely applied due to its ease of installation and quick implementation.

Cellulose is a widely used thermal insulation material made primarily from recycled paper products, such as newsprint and cardboard [109,110,111]. It is treated with fire retardants like boric acid and ammonium sulphate to improve its fire resistance and prevent the growth of mold or pests. As a sustainable and eco-friendly choice, cellulose insulation has gained popularity in both residential and commercial construction due to its excellent thermal properties, soundproofing capabilities, and environmentally friendly production process.

As it is made from up to 85% recycled paper materials, cellulose insulation is one of the most environmentally friendly options available [112,113,114]. Its production requires significantly less energy compared to traditional insulation materials like fiberglass or foam, resulting in a lower carbon footprint. Additionally, using cellulose contributes to waste reduction by repurposing paper products that would otherwise end up in landfills.

Loose-fill application is the most common form of cellulose insulation, often blown into attics, walls, or floors using specialized equipment. The loose-fill material can easily conform to irregular spaces, filling small gaps and voids that might otherwise be difficult to insulate. In the dense-pack method, cellulose is densely packed into wall cavities or other enclosed spaces. The increased density improves its thermal performance and air-sealing properties, making it ideal for retrofitting older homes or for new construction projects.

However, despite its many advantages, cellulose insulation has some limitations. Over time, loose-fill cellulose may settle slightly, potentially reducing its insulating effectiveness, although modern installation techniques have minimized this issue. Additionally, it requires professional installation for most applications, especially for dense-pack and wet-spray methods. While cellulose resists moisture and mold to a certain extent, it should be used with care in areas prone to high moisture levels.

2.4. Twenty-First Century: Sustainable and High-Performance Materials

The 21st century has been marked by significant advancements in thermal insulation materials, driven by rising energy costs, increasing environmental concerns, and the growing demand for energy-efficient buildings. Innovations have focused on enhancing performance and sustainability, as well as addressing climate change through carbon emission reduction and improved energy efficiency. Governments around the world have also introduced stricter building codes and sustainability goals, accelerating the adoption of advanced materials and technologies. Therefore, with the global attention shifting toward sustainable construction and the reduction of carbon emissions, the 21st century has seen the development of new insulation materials and improvements to existing ones that focus on energy efficiency and environmental impacts.

2.4.1. Aerogel Insulation

Aerogels are a type of rigid foam characterized by an exceptionally low density, comprising 90–99.8% air, with the remainder consisting of the porous material that forms its structure [115,116]. The first aerogels, which were prone to collapse, were created by Samuel Stephens Kistler in 1931, but they remained largely forgotten and found few practical applications for a long time. Significant advancements in aerogel development occurred in the second half of the 20th century, particularly during the 1990s when improvements in production techniques enhanced both its properties and availability. Aerogels are renowned for their exceptional thermal insulation capabilities, primarily due to their highly porous structure, which consists of up to 99.8% air. This unique composition results in remarkably low thermal conductivity, making aerogels the materials with the lowest thermal conductivity coefficients among solids, ideal for applications ranging from aviation to building insulation. Additionally, aerogels are lightweight and hydrophobic, further increasing their utility in various industrial and commercial contexts. However, their use as insulating materials in construction is currently limited by their high cost [13,117,118].

2.4.2. Vacuum Insulation Panels (VIPs)

The history of vacuum insulation dates to the late 19th century when James Dewar invented the Dewar flask (later known as the thermos), a double-walled glass cylinder designed to create a vacuum space between its walls by pumping out the air. The concept of vacuum insulation panels (VIPs) has only been applied in construction for a few years. VIPs consist of a rigid or semi-rigid core material, typically made from fiberglass or other lightweight substances, enclosed in a gas-tight barrier [119,120,121]. This barrier is often constructed from aluminum or a polymer foil that prevents air infiltration, creating a vacuum between the core and the barrier. This vacuum significantly reduces heat transfer through conduction and convection, allowing VIPs to achieve thermal conductivities as low as 0.007 W/(mK)—much lower than traditional insulation materials such as fiberglass or foam [11,57].

In Europe, the highest interest in VIPs can be seen in Germany and Switzerland, where they are gaining increasing popularity in the construction industry. More buildings are adopting this modern technology, particularly in situations where space is limited for standard insulation or where a thinner partition is aesthetically preferred. One of the distinguishing features of VIPs is their slim profile, which allows them to provide high insulation values at a fraction of the thickness of conventional materials. This makes them ideal for applications where space is at a premium, such as in energy-efficient buildings, equipment, and transportation systems. However, VIPs do have some limitations, including sensitivity to punctures that can compromise their vacuum seal and reduce their effectiveness, as well as higher production costs compared to traditional insulation materials. Despite these challenges, their exceptional thermal performance and compact design make VIPs an attractive choice for applications requiring the best energy efficiency. Moreover, VIPs help achieve higher energy efficiency while minimizing partition thickness. A significant disadvantage and obstacle to their widespread use in construction is their high cost. However, ongoing research is focused on alternative materials for their construction, which could reduce production costs and make the finished product more affordable in the future [13,122].

2.4.3. Phase Change Materials (PCMs)

Phase change materials (PCMs) represent a cutting-edge innovation in thermal insulation, offering a unique ability to store and release large amounts of thermal energy [123,124,125,126]. They achieve this by absorbing heat during the phase transition from solid to liquid (melting) and releasing it when transitioning back to solid (freezing). This feature enables PCMs to regulate indoor temperatures by capturing excess heat during warmer periods and releasing it as temperatures drop, making them highly effective in improving the energy efficiency of buildings [127,128,129]. By smoothing out temperature fluctuations, PCMs can significantly reduce the demand for heating and cooling systems, which in turn lowers energy consumption. Their ability to store and release thermal energy makes them an ideal component in energy-efficient building designs, aiding in the pursuit of sustainability goals while cutting energy costs [129,130,131,132]. PCMs are particularly beneficial in climates with large temperature variations between day and night. During the day, they absorb and store excess heat, preventing buildings from overheating. At night, they release the stored heat, helping keep the building warm without the need for additional energy inputs. This temperature-balancing capability reduces the reliance on air conditioning and heating systems, making PCMs a cost-effective solution.

PCMs are often integrated into conventional insulation materials, enhancing their thermal performance without compromising the material’s structural integrity or insulation properties. This integration allows for a seamless improvement in energy efficiency within existing insulation frameworks. Despite their many advantages, PCMs do come with some challenges. One drawback is their relatively higher cost compared to traditional insulation materials, which can increase the initial investment. Additionally, PCMs may face issues such as phase separation, subcooling, and long-term stability, particularly with inorganic options. However, ongoing advancements in materials science are helping to address these concerns, making PCMs increasingly workable for widespread use. However, traditional insulation materials with PCMs are at different stages of commercial and technological development [133]. Insulation materials have a long history, with many commercial products readily available, and have been used in construction for centuries [10,13]. In contrast, PCMs have been the focus of intensive research over the past few decades and have been integrated into certain commercial building products [134,135,136]. However, they are not yet as widely adopted as conventional insulation in mainstream construction projects.

PCMs can be effectively incorporated into mineral wool to enhance their thermal performance. When integrated, PCMs significantly boost the heat storage capacity of mineral wool, stabilizing internal temperatures and reducing the need for heating and cooling. Studies have shown that this combination is particularly effective in regulating temperature fluctuations in buildings located in regions with extreme climates. This makes PCM-enhanced mineral wool an excellent solution for both residential and commercial buildings striving for higher energy efficiency. Another promising application of PCMs is in foam concrete [124,133,136]. Known for its lightweight and insulating properties, foam concrete benefits greatly from the addition of PCMs, which further improve its ability to regulate heat. PCMs embedded in foam concrete panels absorb and release heat during phase transitions (from solid to liquid and vice versa), allowing for the maintenance of more consistent indoor temperatures. This reduces the reliance on HVAC systems, thereby lowering overall energy consumption. Research has shown that foam concrete with PCM enhances thermal inertia and delays heat transfer, making it ideal for regions with significant temperature swings.

Both applications—PCMs in mineral wool and foam concrete—demonstrate the potential for PCMs to elevate the performance of conventional insulation materials, contributing to more sustainable and energy-efficient building practices.

2.4.4. Other Materials

Furthermore, in the 21st century, the previously developed materials continue to develop, with a focus on improving performance, environmental impacts, and fire safety. In this regard, polyurethane and PIR foams, which were developed in the mid-20th century, have been improved in the 21st century to provide better thermal performance, fire resistance, and environmental safety. Advances in the formulation of these materials have led to the development of foams with higher R-values (thermal resistance), making them more efficient at insulating buildings. Additionally, the use of environmentally friendly blowing agents has reduced the ozone-depleting potential of foam insulation products, aligning with the stricter environmental regulations.

In response to growing environmental concerns, the insulation industry has also introduced bio-based foam insulation materials. These foams are made from renewable resources, such as soybean oil or castor oil, instead of petrochemical-derived ingredients. Bio-based foams offer similar insulating properties to traditional foam insulation but with a lower carbon footprint. The development of low-VOC (volatile organic compound) and non-toxic foam insulation products has also become a priority, particularly for improving indoor air quality in green buildings.

Further, sustainability and the circular economy have become central themes in the 21st century, leading to increased interest in natural and recycled insulation materials. These materials offer the dual benefit of being eco-friendly while providing effective thermal insulation.

Hence, cellulose, made from recycled paper, has gained renewed attention in the 21st century due to its environmental benefits. It is a highly sustainable insulation option, with low embodied energy, and can be treated with fire-retardant chemicals to improve its safety. Cellulose is commonly used in both new construction projects and retrofitting older buildings, providing a sustainable alternative to synthetic insulation materials. Similarly, natural fiber insulation such as wool, hemp, or cotton have seen increased adoption in the 21st century, particularly in sustainable and green building projects. Wool, hemp, and cotton are renewable resources that offer good insulating properties, breathability, and moisture regulation. These materials are also biodegradable and non-toxic, making them a healthier choice for indoor environments. Though more expensive than traditional insulation options, natural fiber insulation appeals to environmentally conscious consumers and builders. Recycled plastic insulation materials, such as polyester made from recycled PET bottles, are also being used although they have become a problem in the 21st century.

2.5. Recap of Historical Milestones and Current Works

The development of thermal insulation materials discussed in the previous sections is summarized in

Table 1. Thermal insulation material development.

Century	Material Type
Ancient Times	Natural materials: wool, straw, mud, leaves, and reeds; materials with a high thermal mass such as stone and wood
19th and Early 20th	Cork, insulation materials from wood waste, wood wool, and asbestos
Mid- and late 20th Century	Mineral wool, fiberglass, foam glass, plastic foams, and cellulose
21st Century	Aerogels, vacuum insulation panels, functional materials with phase change materials (PCMs)

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In past years and nowadays, there is still a significant interest in the research and development of thermal insulation materials, driven by the increasing demand for energy efficiency, sustainability, and improved building performance. As global energy consumption rises and climate change concerns escalate, researchers are exploring innovative materials and technologies that enhance thermal performance while minimizing environmental impacts. This includes the development of advanced insulation solutions, such as aerogels and vacuum insulation panels, as well as sustainable alternatives made from recycled materials and natural fibers. Furthermore, ongoing studies are focusing on improving the fire resistance, durability, and moisture management of insulation materials, ensuring that they meet modern building codes and standards. Integrating smart technologies, such as phase change materials (PCMs) and responsive insulation systems, is also gaining traction, enabling buildings to adapt to fluctuating temperatures. Overall, the sustained interest in thermal insulation research reflects a collective commitment to creating more energy-efficient and environmentally friendly building practices. It is worth noting that, according to the Science Direct database, 17,166 works on thermal insulation were published in 2024, with 387 publications already available for 2025. For this reason, only selected publications from 2024 [107,129,137,138,139,140,141,142,143,144,145,146,147,148] and 2025 [149,150,151,152,153,154] can be mentioned. This summary underscores the field’s dynamic nature and reflects the current research in thermal insulation materials.

3. Properties and Performance Criteria of Insulation Materials

The need for thermal insulation materials is critical worldwide, but specific requirements vary greatly depending on the regional climate. In cold climates such as Canada and the Scandinavian countries, prolonged and severe winters necessitate materials with high thermal resistance to minimize heat loss. Additionally, these materials must be durable enough to withstand harsh weather conditions and effectively control moisture to prevent condensation and mold growth. Common insulation materials in these regions include fiberglass, mineral wool, polystyrene foam, and polyurethane foam.

In temperate climates, found in parts of the United States, Central Europe, and China, seasonal temperature fluctuations create moderate heating and cooling demands. Here, a balance of insulation performance, energy efficiency, and cost-effectiveness is essential. Fiberglass, cellulose, mineral wool, and expanded polystyrene (EPS) are commonly used. Hot climates, such as those in Saudi Arabia, Australia, and India, experience extreme heat and high cooling costs. These climates need insulation materials with reflective, moisture-resistant, and fire-resistant properties, such as reflective insulation, radiant barriers, foam board, and spray polyurethane foam (SPF). In humid climates, including Brazil, Southeast Asia, and the southern United States, high humidity and variable temperatures require insulation that effectively manages moisture, prevents air infiltration, and resists biological growth. Common choices include closed-cell spray foam, rigid foam insulation, and fiberglass with vapor barriers. Mixed and transitional climates, found in regions with significant climatic variations—such as parts of the United States, Japan, and Mediterranean countries—demand flexible insulation that performs well under diverse conditions. Thermal mass materials and versatile multi-layer systems are typically employed. Understanding these climatic differences is essential for selecting the proper insulation materials that ensure energy efficiency, comfort, and durability in buildings, ultimately contributing to sustainable development and resilience. It is important to note that the requirements in various countries may differ and are continuously evolving. Since 2013, the standards for the thermal insulation of external walls, roofs, floors, windows, and doors have been gradually tightened.

Table 2. Evolution of requirements for thermal insulation, based on Poland’s regulations.

Type of Barrier (ti—Indoor Temperature)	Heat Transfer Coefficient U, W/(m2·K)
	Up to 31 December 2013	From 1 January 2014	From 1 January 2017	From 1 January 2021
External walls:
(a) ti ≥ 16 °C	0.28	0.25	0.23	0.20
(b) 8 °C ≤ ti < 16 °C	0.65	0.45	0.45	0.45
(c) ti < 8 °C	0.90	0.90	0.90	0.90
Roofs, flat roofs, and ceilings under unheated attics or above passages:
(a) ti ≥ 16 °C	0.25	0.20	0.18	0.15
(b) 8 °C ≤ ti < 16 °C	0.50	0.30	0.30	0.30
(c) ti < 8 °C	0.70	0.70	0.70	0.70
Floors on the ground:
(a) ti ≥ 16 °C	0.45	0.30	0.30	0.30
(b) 8 °C ≤ ti < 16 °C	1.20	1.20	1.20	1.20
(c) ti < 8 °C	1.50	1.50	1.50	1.50
Ceilings above unheated rooms and enclosed underfloor spaces:
(a) ti ≥ 16 °C	0.45	0.25	0.25	0.25
(b) 8 °C ≤ ti < 16 °C	1.20	0.30	0.30	0.30
(c) ti < 8 °C	1.50	1.00	1.00	1.00

illustrates this evolution, using Poland as an example. Therefore, as the years went by, the values of the heat transfer coefficient evolved, causing the adoption of increasingly advanced thermal insulation materials with improved performance characteristics.

Thermal insulation is defined as a layer of material with low thermal conductivity, which is designed to reduce unwanted heat exchange with the environment. In construction, it refers to materials that minimize heat transfer through structural elements such as walls, roofs, floors, and ceilings. The primary goal of thermal insulation is to keep a constant and comfortable indoor temperature, regardless of external weather conditions. Additionally, the need for thermal insulation is often driven by legal requirements concerning the right heat transfer parameters for external partitions. The importance of thermal insulation can be summarized as follows:

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Thermal comfort: The maintenance of a stable indoor temperature, enhancing user comfort by preventing cold or excessively heated external surfaces.

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Building integrity: Proper thermal insulation protects the building structure from damage caused by temperature fluctuations and moisture condensation. It also helps prevent thermal bridging, local dampness, and mold development.

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Energy savings: A well-insulated building consumes less energy for heating in winter and cooling in summer, leading to lower energy consumptions.

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Environmental protection: Reducing energy consumption for heating and cooling decreases greenhouse gas emissions, which are significant contributors to climate change.

When selecting insulation materials for external partitions, it is crucial to consider the thermal conductivity coefficient (λ), which indicates the material’s thermal insulation properties. A lower λ value signifies a better insulation performance and reduced heat loss. Currently, the thermal conductivity coefficient of available insulation materials typically ranges from 0.045 to 0.020 W/(mK).

Table 3. Thermal characteristics of different insulation materials.

Category	Material Type	Thermal Conductivity (λ), W/(mK)	Thermal Characteristics	Examples	Intensity of Use in Building Insulation
High Thermal Resistance	Low thermal conductivity	0.020–0.025	High R-value (resistance to heat flow)	Polyisocyanurate, polyurethane foams	High
Moderate Thermal Resistance	Balanced thermal properties, suitable for various applications	0.035–0.045	Moderate R-value	Fiberglass, foam glass, mineral wool	Widely used
Low Thermal Resistance	Higher thermal conductivity, typically used in specific contexts	0.050–0.075	Lower R-value, used where insulation is not the primary concern	Stone wool, certain types of polystyrene	Moderate
Phase Change Materials (PCMs)	Absorb and release thermal energy, helping to regulate temperature	0.100–0.200	Change phase at specific temperatures, improving comfort and energy efficiency	Paraffin wax	Low (new technology)
Reflective or Radiant Barriers	Reflect radiant heat rather than absorbing it	0.002–0.005	High energy efficiency	Radiant barrier foil, reflective insulation	Moderate
Composite Materials	Combine different insulation properties	0.020–0.045	Optimized thermal resistance for specific applications	Structural insulated panels	Moderate to High (increasing popularity)
Natural Fiber Insulation	Derived from natural sources; offers moderate thermal performance	0.035–0.045	Effective insulation with additional benefits like breathability	Sheep wool, cotton, hemp, cork	Low to moderate (niche markets)
Aerogels	Extremely low-density materials with exceptional thermal insulation properties	0.007–0.020	Very low thermal conductivity; lightweight	Silica aerogels, polymer-based aerogels	Low (specialized applications)
Recycled Materials	Made from recycled content, offering variable thermal characteristics	0.040–0.055	Varies based on composition; often moderate thermal resistance	Recycled cellulose, denim insulation	Growing (increasing interest in sustainability)

provides a clear overview of the thermal conductivity values along with the thermal characteristics of different insulation materials [13,155].

Other important factors to consider when choosing insulation materials, depending on their application, include hardness, bulk density, acoustic insulation, and water absorption, resistance to mechanical damage, and the conditions and methods of installation.

An extremely important factor influencing the choice of insulation in modern construction is the fire resistance of thermal insulation materials. Fire classification, or fire reaction class, designates how materials behave when exposed to fire and is based on the EN 13501 standard, which is used across the EU [156]. This classification involves the basic classes (A to F), additional criteria for smoke emission, and burning droplet criteria. When evaluating fire-resistant insulation, properties such as thermal stability, low flammability, and minimal smoke production are key. Fire-resistant insulation helps contain flames, maintain structural integrity, and reduce toxic smoke emissions, protecting occupants and reducing damage. Materials classified as A1, like glass and rock mineral wool, are non-flammable and highly fire-resistant, making them ideal for minimizing fire spread and ensuring safety. In contrast, flammable materials like polyurethane and polystyrene, classified as E or F, are less fire-resistant and more hazardous. The use of fire-resistant insulation not only enhances safety and minimizes damage but also ensures compliance with building codes, safeguarding both property and lives during a fire. Therefore, the fire resistance of thermal insulation materials is not just a feature but a fundamental requirement for ensuring the safety of occupants, protecting property, and meeting building regulations. In fire-prone or high-risk environments, selecting the proper fire-resistant insulation can make a critical difference in how well a building or industrial facility performs under fire conditions. The fire resistance characteristics of common thermal insulation materials of the basic classes are summarized in

Table 4. Fire resistance characteristics of common thermal insulation materials.

Fire Resistance Class	Material Type	Description
A1 (non-combustible)	Glass Mineral Wool	Non-flammable: does not contribute to fire development or flame spread.
	Rock Mineral Wool	Similar to glass wool: excellent fire resistance and thermal stability.
A2 (limited combustibility)	Wood Wool	Nearly non-flammable: may emit negligible heat in intense fire conditions.
B (combustible with limited flame spread)	Polyurethane Foams	Provides insulation but has some combustibility; may emit smoke under fire.
C (combustible)	Expanded Polystyrene (EPS)	Flammable: can contribute to flame spread but often treated to reduce risk.
	Polyurethane Foam (PUR)	Self-extinguishing but can be highly flammable; treated products are available.
D (highly combustible)	Fiberglass	May contribute to flame spread.
E (flammable)	Some Spray, Foam Insulation, Cork	Combustible and can produce smoke; not recommended for high-risk areas; cork burns slowly and does not contribute significantly to the spread of fire; the gases are not toxic
F (non-combustible)	Certain Low-Quality Foam Products	Can easily ignite and may contribute significantly to fire spread.

Comments: The A1 and A2 classes are the safest and recommended for high fire-risk environments. Materials classified as B and C require careful consideration and often require additional fire-retardant treatments. Classes D, E, and F indicate materials that are more hazardous in fire situations and may not be suitable for certain applications without proper fire safety measures. Local building codes and regulations should always be referred to for specific requirements regarding fire resistance of insulation materials.

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The next important issue in the analysis of thermal insulation materials relates to the environmental impact of the thermal insulation materials which is a critical consideration in sustainable construction. When assessing the environmental footprint of insulation materials, it is essential to consider the full life cycle of these products, including their production, use, recycling, and disposal. This life cycle assessment (LCA) evaluates the environmental performance of materials from raw material extraction through the manufacturing, installation, operation, and end-of-life stages [16,17,18,133,157]. Therefore, LCA provides a comprehensive framework for the evaluation of the environmental impacts of thermal insulation materials over their entire lifespan. At the production stage, the raw materials used in the insulation can contribute to significant environmental impacts through resource extraction, energy use, and pollution. For example, mineral-based materials such as glass wool and rock wool require substantial energy at the production stage, contributing to greenhouse gas emissions. However, the energy saved during the operation of buildings—through reduced heating and cooling demands—often outweighs the emissions from production over the insulation’s lifetime. LCAs help identify these trade-offs and enable a more informed selection of materials that balance the initial environmental impacts with long-term benefits.

Simultaneously, incorporating the 6R principles into the design, production, and end-of-life management of insulation materials can help minimize their environmental impact. Incorporating the 6R principles into the design, production, and end-of-life management of insulation materials can help minimize their environmental impact. For instance, reducing the amount of non-renewable or toxic materials in insulation products and prioritizing renewable, biodegradable, or recycled materials can significantly lower their environmental footprint. The 6R principles can be related to the thermal insulation materials as follows:

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Reduce refers to minimizing the amount of material used, which can lower the environmental impact during production and reduce waste generation.

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Reuse involves extending the life of insulation materials by using them in multiple projects or applications, reducing the demand for new resources.

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Recycle focuses on reclaiming insulation materials at the end of their life cycle, processing them into new products, and closing the resource loop.

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Recover suggests utilizing energy recovery processes for materials that cannot be recycled, such as burning waste insulation in controlled conditions to generate energy.

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Redesign encourages the development of new insulation materials that are easier to recycle, more durable, and less harmful to the environment.

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Rethink promotes a shift in how we approach insulation, advocating for more sustainable materials, better design practices, and more efficient use of resources.

Incorporating the 6R principles into the design, production, and end-of-life management of insulation materials can help minimize their environmental impact. For instance, reducing the amount of non-renewable or toxic materials in insulation products and prioritizing renewable, biodegradable, or recycled materials can significantly lower their environmental footprint. In this context, recycling and utilization are increasingly important in managing the environmental impact of insulation materials. Some materials, like mineral wool, can be recycled, reducing the need for virgin materials and minimizing waste. However, certain types of insulation, particularly those made from plastic polymers like polystyrene or polyurethane, are more challenging to recycle due to the difficulty of separating and processing them. The recycling rates for these materials are often low, leading to significant amounts of construction waste that end up in landfills. Expanding recycling infrastructure and developing new technologies for handling complex materials are crucial steps toward reducing the environmental footprint of insulation materials. Incorporating recycled content into the production of insulation materials can also lessen the reliance on raw material extraction and reduce the associated environmental impacts.

Reusing insulation materials offers another sustainable option that helps reduce waste and conserve resources. Certain materials, such as rigid insulation boards, can be removed and reused in other projects without losing their insulating properties. This practice aligns with the principles of a circular economy, where materials are kept in use for as long as possible to minimize waste and environmental harm. Reusing insulation can also lower the demand for new materials, conserving resources and reducing the energy and emissions associated with manufacturing. Simultaneously, reusing is unfortunately associated with several challenges. It is a complex process that requires the consideration of multiple factors, including functional, aesthetic, legal, economic, and social aspects, as well as, most importantly, technical and technological ones. A common issue with reusing materials is determining their current technical condition, specifically, how well they retain their original properties. Legal factors, such as certification, approval for use, and safety compliance, along with the technical standards mandated by regulations, play a significant role in ensuring the viability of reused components.

Durability is also a key factor in assessing the environmental impact of insulation materials. Materials that last longer and maintain their insulating properties over time reduce the need for replacement, leading to lower environmental costs over the building’s lifespan. Generally durable materials, like rock wool and fiberglass, have lifespans that often exceed 50 years, meaning that their environmental impacts are amortized over a long period. Conversely, insulation materials that degrade or lose effectiveness may require more frequent replacement, leading to higher material consumption, increased waste, and a greater environmental impact over time. At the same time, the durability of insulation systems is influenced by various factors such as water, wind, temperature fluctuations, and moisture sensitivity. Climate change can harm insulation materials, especially cellulose used in timber frame structures. High-humidity environments can promote fungal growth, which deteriorates both the durability and thermal performance of insulation. Additionally, the age of the insulation and the loads it bears throughout its lifespan—such as exposure to fluctuating temperatures, sunlight, mechanical damage, and the activity of rodents and insects—can significantly accelerate degradation.

Further, the type of insulation material plays a critical role in its long-term durability. For example, natural fiber-based insulation is more sensitive to moisture, leading to a reduction in thermal performance under high humidity conditions. When selecting insulation materials, it is also important to consider their compatibility with nearby materials, such as wood. Proper insulation selection in proximity to wood is crucial to prevent damage that could compromise the structural integrity of wooden elements. Conversely, plastic-based insulation materials may degrade when exposed to chemical reagents found in adjacent building materials, such as tar, roofing felt, or adhesives. In building insulation systems that utilize the “light-wet” method—where the insulation layer is protected by a thin layer of adhesive and plaster—the materials are not only vulnerable to mechanical damage but also to thermal shock. During the day, the façade may be heated to high temperatures, especially for those with darker colors, reaching up to 90 °C on southern exposures in summer and over 80 °C on eastern and western exposures. Such extreme temperatures can exceed the softening points of common materials like polystyrene (80 °C) and PVC (78 °C), leading to deformation. Sudden cooling, for instance, from a storm or rainfall, can cause rapid contraction, cracking the plaster and delaminating façade elements. Once this protective layer is compromised, the underlying insulation is exposed to environmental factors, accelerating its degradation, regardless of whether polystyrene or mineral wool is used.

Further, permeability to water vapor, which was mentioned in the Introduction, is also a crucial characteristic of thermal insulation materials and should be thoroughly addressed as it directly impacts both the performance of the material and the indoor environmental conditions. In materials with high permeability, such as cork and mineral wool, moisture is allowed to diffuse through the building envelope, which helps balance indoor humidity and prevent the buildup of trapped moisture. This is especially important in regions with significant temperature fluctuations, where condensation can form inside wall cavities if vapor is not properly managed. On the other hand, insulation materials with low permeability, such as extruded polystyrene (XPS) and closed-cell foam boards, offer high resistance to water vapor, which can be beneficial in environments where moisture ingress must be minimized. However, in these cases, additional measures like vapor barriers or proper ventilation are needed to control moisture levels and ensure that the building remains dry and healthy. Therefore, the choice of insulation material must be aligned with the specific climate and the building’s design to ensure a balance between thermal insulation, vapor diffusion, and indoor comfort. It is crucial to highlight the importance of selecting materials that not only provide thermal resistance but also contribute to healthy indoor environments by preventing moisture problems, which can lead to structural damage and mold growth. This will result in more sustainable and durable buildings that perform well under a variety of environmental conditions. The proper management of water vapor permeability in insulation materials helps maintain optimal indoor humidity levels, preventing mold growth and improving the overall indoor air quality. By considering this property, insulation systems can enhance thermal comfort while avoiding moisture-related problems that could compromise both the building structure and the health of occupants.

The service life of insulation materials is thus determined by a complex interplay of environmental conditions, material properties, design choices, and maintenance practices. A proper understanding of these factors and selecting insulation materials with durability in mind are essential to ensuring the long-term performance of building insulation systems. Developing advanced and cost-effective, high-performing, and degradable insulation materials is crucial to extending the lifespan of insulation in buildings and enhancing their overall sustainability.

Ultimately, to minimize the impact of thermal insulation materials on the environment, a holistic approach that considers their full life cycle, along with their recyclability, reusability, durability, and adherence to the 6R rules, is essential. By focusing on these factors, the construction industry can create more sustainable buildings that not only conserve energy but also reduce waste, emissions, and resource consumption. A brief overview of the recyclability of various thermal insulation is summarized in

Table 5. The recyclability of various thermal insulation materials.

Category	Material	Recyclability
Natural Materials	Wool	Biodegradable; can be composted or recycled.
	Cotton
	Hemp
	Straw Cork
Wood-Based Materials	Wood Fiber	Recyclable; can be processed into new products.
	Wood Wool Cork
Mineral-Based Materials	Mineral Wool (Rock Wool)	Difficult to recycle; some facilities may reclaim.
	Glass Wool
Synthetic Materials	Expanded Polystyrene (EPS)	Recyclable; can be processed into new EPS products.
	Extruded Polystyrene (XPS)	Limited recyclability; can be downcycled in some cases.
	Polyurethane Foam	Difficult to recycle; often ends up in landfills.
Composite Materials	Bio-based Composites	Can be recycled depending on components.
Recycled Materials	Recycled Cotton Batts	Recyclable; made from post-consumer textiles.
	Recycled Plastic Insulation	Recyclable; made from post-consumer plastic waste.
Non-Recyclable Materials	Asbestos	Hazardous; requires specialized disposal methods.

.

The specificity of historical buildings should be also mentioned. Improving the energy efficiency of historical buildings, including listed ones, is often a challenging task. Due to decorative facades and specific architectural details, using external insulation materials is not always feasible without compromising the architectural and historical integrity of the building. In such cases, internal insulation should be considered. However, this approach presents the risk of water vapor condensation within the wall partitions, particularly when conventional insulation materials such as polystyrene, polyurethane, or mineral wool are used. These solutions can lead to mold growth and the migration and crystallization of mineral salts, which cause material corrosion. To mitigate these risks, more specialized options such as lime silicate boards, volcanic-origin perlite boards, vacuum panels, or mineral insulation boards can be used for internal wall insulation.

4. Classifications

Thermal insulation materials can be classified based on several criteria, including their composition, structure, application, as well as specific properties. One common method of classification is by material type, which includes organic materials (such as cellulose and wood fiber), inorganic materials (such as mineral wool and polystyrene), and synthetic materials (such as fiberglass and polyurethane). Another classification method is based on the insulation mechanism, distinguishing between reflective insulation, which relies on reflective surfaces to minimize radiant heat transfer, and bulk insulation, which traps air to reduce conductive heat transfer. Additionally, insulation materials can be categorized by their physical form, including batts, rolls, loose fill, and rigid boards, each suited for specific installation methods and applications. Finally, thermal performance, often measured by thermal conductivity, R-values, or U-values, can also serve as a basis for classification, with materials grouped according to their effectiveness in resisting heat flow. This diverse classification was already mentioned and outlined in the earlier sections.

The additional classification of thermal insulation materials in light of the current trends in modern construction and growing environmental considerations is provided in

Table 6. Summary of current trends for thermal insulation materials.

Trend/Need	Description	Examples
Sustainability	Eco-friendly, sustainable materials.	Recycled materials; bio-based insulation; cork
Energy Efficiency	Materials that enhance energy efficiency in buildings.	Vacuum insulation panels (VIPs); aerogels; PCMs; reflective foil-faced boards or blanket
High Thermal Performance	Materials with superior insulation properties.	Vacuum insulation panels (VIPs); aerogels; reflective foil-faced boards or blanket
Indoor Air Quality	Materials that contribute to better indoor air quality.	Natural fibers; low-VOC (volatile organic compound) materials; cork
Moisture Release	Moisture-resistant materials to prevent mold growth.	Hydrophobic insulation; breathable membranes
Fire Resistance	Materials that offer improved fire resistance.	Glass mineral wool; rock mineral wool
Lightweight Solutions	Lighter materials to reduce structural load.	Expanded polystyrene (EPS)
Cost-Effectiveness	Need for affordable insulation solutions without compromising quality.	Recycled cellulose; low-cost foams
Biodegradability	Materials that can naturally decompose.	Hemp; wool; cork
Smart Insulation	Integration of technology for adaptive insulation properties.	Phase change materials (PCMs)
Modular Design	Modular construction with adaptable insulation.	Insulated panels for prefabricated units, cork panels; reflective foil-faced boards or blanket
Regulatory Compliance	Need to meet building codes and energy standards.	Building standards; other certifications (e.g., LEED, BREEAM)

. As the demand for energy efficiency and sustainable building practices intensifies, insulation materials are being evaluated not only for their thermal performance but also for their ecological impact. This has led to a greater emphasis on the development of eco-friendly materials, such as those derived from recycled products or natural fibers, which align with the principles of sustainable construction. This classification not only facilitates the selection of appropriate materials but also reflects the broader shift towards environmentally responsible construction practices in today’s building industry.

5. Conclusions

This review outlined the historical evolution and current trends in thermal insulation materials, illustrating the advancements in building technologies and the growing focus on sustainability. The role of thermal insulation has always been crucial, and it will continue to be indispensable in reducing energy consumption, enhancing indoor comfort, and supporting environmental goals, particularly in the face of climate change and the rising energy costs. The development of thermal insulation materials can be divided into four key periods, each marking significant milestones in their advancement.

The first period relates to ancient materials such as straw, wool, and mud, which provided basic thermal comfort and protection. During the Industrial Revolution in the 19th and early 20th centuries, mass production capabilities enabled the widespread use of more effective materials like cork, asbestos, and mineral-based insulators. This period also introduced technological breakthroughs that allowed for the efficient processing of materials like cork. In the mid- to late 20th century, thermal insulation materials underwent a wave of innovation, driven by rising energy demands. The introduction of mineral wool, fiberglass, and synthetic foams like polyurethane and polystyrene revolutionized the construction industry. These materials offered superior thermal performance, durability, and adaptability to modern construction practices, making them popular choices in both residential and industrial settings. The transition from natural to synthetic insulation materials has provided significant benefits in terms of thermal performance, durability, and cost-effectiveness. However, these gains have come at a considerable environmental cost, including increased energy use, waste accumulation, and the release of harmful chemicals. The 21st century has seen a substantial shift towards sustainability, driven by global regulations like the European Climate Law, which mandates a 55% reduction in greenhouse gas emissions by 2030. This shift has induced the development of high-performance, eco-friendly insulation solutions. Innovations such as aerogels, vacuum insulation panels (VIPs), and phase change materials (PCMs) have emerged as cutting-edge technologies offering exceptional thermal efficiency while minimizing the environmental impact. Additionally, there has been growing interest in bio-based and recycled materials such as cellulose, hemp, cork, and sheep wool, reflecting the broader push towards resource conservation and circular economy principles.

An essential aspect of modern insulation materials is the integration of the 6R principles—reduce, reuse, recycle, recover, redesign, and rethink—into their design and life cycle management. This focus ensures that materials not only deliver high thermal performance but also contribute to long-term sustainability. Recyclability and reusability are now key factors in the selection of insulation products, along with their durability, fire resistance, and impact on indoor air quality. As a result, the construction industry is increasingly prioritizing materials that align with these principles, ensuring that they can be reused, recycled, or decomposed with minimal harm to the environment.

The evolution of thermal insulation materials reflects humanity’s broader progress in addressing energy efficiency, environmental sustainability, and building performance. From natural fibers and mineral-based solutions to the most advanced synthetic and bio-based materials, each era has introduced new solutions to meet the growing demand for energy conservation and comfort. Looking ahead, the future of thermal insulation lies in the continued development of sustainable, high-performance materials that address both environmental concerns and energy efficiency. In conclusion, the ongoing improvement of insulation materials is not just about meeting regulatory requirements or reducing energy bills; it is about shaping healthier, more sustainable living environments. By embracing technological innovation and sustainable practices, the industry can help combat climate change, reduce greenhouse gas emissions, and build a greener future for generations to come.