Thermochromic Yarns’ Application in Fever Detection for Young Children

Abstract

The existing literature emphasizes the significance of and needs for developing body temperature monitoring devices that can consistently and discreetly assess the temperatures of young children. Such products could offer a method to check children’s body temperature and alleviate parents’ concerns over fever. However, research gaps and challenges exist in preserving material flexibility, conducting tests in a controlled setting that mimics body temperature, and investigating consumer perceptions of this type of functional textile product. Therefore, this research aimed to investigate functional textiles using thermochromic yarns for young children’s body temperature detection, particularly focusing on testing prototypes in a controlled environment and empirically investigating target consumers’ perceptions of such products. Experimental prototype testing and a consumer survey were conducted in this study. The findings validate the practicality and market potential of such products. We also proposed alternative mediums for implementing the functional yarn and recommendations for developing these products based on target consumers’ concerns and suggestions. This research helped identify potential economic development possibilities for functional textiles.

1. Introduction

Parents prioritize good health as the most crucial factor for their young children. Integrating sensing functions in children’s clothing to monitor vital signs such as blood pressure [1], pulse, respiratory rate [2], temperature [3], and heartbeat [4] allows for early detection of potential health risks with the potential of obeying the safety protocols [5]. These goals can be achieved using functional and smart textiles, allowing for real-time biological signal monitoring [6]. Ghosh et al. [7] define functional textiles as those primarily valued for their technical performance and functionality rather than aesthetics, and smart textiles as a subset of functional textiles that can detect and interpret signals to respond accordingly. For example, Jabubas and Łada-Tondyra [8] developed a method to measure respiratory rhythm using knitted fabric made of electrically conductive strands integrated into baby underwear, which can help detect respiratory disorders like asthma, choking, and Sudden Infant Death Syndrome (SIDS).

Among all of the vital signs, monitoring young children’s body temperature is especially important because it indicates infection and the infant’s overall well-being. This metric is also utilized to determine the ideal temperature of the environment for the optimal growth of infants [3]. Fever phobia, initially described by Schmitt [9], reflects parents’ heightened anxieties about their child’s body temperature. Parents intend to control their young children’s temperature to prevent febrile convulsions, brain damage, and pain, and to enhance their overall well-being [10]. Childhood fever impacts parents in socio-economic, physical, and emotional ways. Parents of children with a fever may need to take time off work, consult a doctor, buy medications, and require additional help at home. Fear of baby fever can heighten parents’ physical and mental strain, leading to frequent temperature monitoring, anxiety, and sleep disturbances [11]. Therefore, researchers have been exploring textile-based solutions for temperature measurement that track body temperature continuously and unobtrusively [3]. The current predominant methods for monitoring temperature in smart textiles rely on traditional sensors such as thermo-elements, thermistors, and semiconductor sensors [5]. Traditional sensors on clothing are attached to the fabric rather than integrated into it, leading to substantial discomfort for users and skin irritation due to their rigidity [6]. Other challenges of traditional sensors in smart textile solutions for monitoring temperature include battery size, energy suitability, and washability. Some require removing the electronic components before washing [6].

Alternatively, researchers have been exploring functional textiles to detect body temperature changes, including thermochromic materials. Thermochromism is the reversible alteration in a compound’s colour triggered by a temperature change, with the colour shift being obvious, sometimes dramatic, and happening within a narrow temperature range [12]. Thermochromism occurs due to various mechanisms based on the compound’s molecular structure. The thermochromic mechanism can be categorized into three main groups: change in crystal structure, stereoisomerism, and molecular rearrangement [13]. To be used in textiles to detect body temperature, the component must (1) have a reversible and solid (or encapsulated) system that is appropriate for dyeing and printing, (2) display a distinct colour change within a narrow temperature range, usually from low ambient temperatures to body temperature, and (3) be cost-effective [14,15]. These criteria make the molecular rearrangement mechanism, where temperature changes lead to a molecular rearrangement in a compound, causing an increase in conjugation within the molecule and the creation of a new chromophore, resulting in a colour change, the most achievable option [13]. However, thermochromic materials cannot dye the fibre directly due to their lack of affinity with it, necessitating microencapsulation [16].

Potuck et al. [17] applied thermochromic pigments to sportswear to visually spot muscle fatigue by observing colour changes in the garment as the skin temperature rises. A thermal manikin set in a controlled environment validated the pigment colour change. The manikin simulated the average skin temperature according to ISO standards and replicated a high skin temperature. While the garment reacted appropriately to the temperature change, the thermochromic coating caused the fabric to curl naturally, making it challenging to stitch evenly. The increased thickness of the fabric made the garment’s breathability questionable. Zou and Feng [18] studied thermochromic materials for monitoring newborns’ temperature by utilizing thermochromic fabrics through printing, sewing, and knitting techniques. They conducted interviews, testing, and prototyping to assess and validate the adaptability of the product concept. Their research explored various prototyping concepts utilizing thermochromic materials. However, testing was not conducted at skin temperature, making it impossible to determine if the prototype could effectively detect fever.

While much research exists on innovative textiles and applications, researchers often focus solely on developing new products without exploring consumer perceptions of them [6]. Ju and Lee [19] identified various obstacles affecting consumers’ interest in smart clothing, including but not limited to safety, functionality, availability, reliability, price, aesthetics, and size. Bergmann and McGregor [20] found that users prefer a body-worn sensor system that is compact, embedded, and simple to operate and maintain. While Zou and Feng [18] conducted interviews with consumers, the discussion was mainly on how consumers react to the importance of body temperature monitoring instead of their attitudes towards the prototype ideas. Consequently, due to their current absence, it is critical to incorporate consumer preference investigations into developing new smart and functional textile goods [20].

A literature analysis highlighted the necessity of creating body temperature monitoring devices that can continually and inconspicuously measure the temperatures of young children. Such a product will ease parents’ worries about fever and provide a means to monitor their children’s body temperature. Advanced textiles, such as smart textiles or functional textiles, have the potential to provide answers because of their flexibility and ability to be worn near the body. Because incorporating electrical devices into smart textiles has posed difficulties regarding comfort and washability, researchers have investigated functional textiles using thermochromic mechanisms to monitor body temperature. Nevertheless, current studies on thermochromic fabrics encountered difficulties in maintaining material flexibility [17], conducting tests in a simulated body temperature environment [18], and exploring consumer perceptions of such products [17,18]. Therefore, this research aimed to investigate thermochromic yarns’ application in fever detection for young children, particularly focusing on testing prototypes in a controlled environment, simulating fever and non-fever conditions, and empirically investigating target consumers’ perceptions of such products. More precisely, two research questions (RQ) were formulated:

RQ1. Is it feasible to utilize yarns coated with encapsulated thermochromic pigment to create a knitted structure to detect a body surface’s elevated temperature (fever)? If so, how would the variation in colour change (fever vs. non-fever) differ across various aesthetic settings?

RQ2. How do prospective buyers see the fever-detecting prototype being used for young children?

In the following sections, we first explained the materials employed in this research, including the design prototype and knitted samples utilized to assess performance. Subsequently, we disclosed the data collection and analysis approach to tackle the research questions. The results and discussion section responded to the research questions. The conclusion section offered a concise summary of the research’s contribution. Finally, researchers identified limits that would shape the focus of future studies.

2. Materials and Methods

2.1. Prototyping

Fever is characterized as an increase in body temperature that exceeds the typical daily variation. The core temperature is usually defined as the temperature measured inside the pulmonary artery. However, because of the impracticality of accessing deep tissue measuring locations, physicians have resorted to using alternative sites such as the axilla, skin, beneath the tongue, rectum, and tympanic membrane to monitor body temperature [21]. Forehead thermometers are used at home because of their advantages of convenient instruction, ease of use, safety, comfort, and rapid results [21]. Thus, the designed prototype opted to monitor the body temperature of young children by focusing on the forehead.

The newborn’s head plays a crucial part in controlling his/her body temperature because of the heat produced by the brain and the heat loss from its surface area. Stothers [22] discovered that wearing a hat can significantly reduce infant heat loss. This is potentially associated with the risks of hypothermia, a significant and potentially dangerous drop in body temperature. Therefore, the designed prototype utilized a hat as the medium for applying the thermochromic materials. Figure 1 illustrates the sketch and working mechanism of the fever monitor hat designed for young children.

We investigated the thermochromic yarn market and identified a provider, Jinhaosheng Textile Co. Ltd., that sold synthetic yarns coated with encapsulated thermochromic pigment in various colours. The supplier also allowed us the opportunity to customize the temperature at which the colour change occurred. The yarn is composed of synthetic materials with a 250/2 Denier weight and possesses a somewhat rigid texture. This aligns with the research conducted by Potuck et al. [17], who discovered that a thermochromic coating stiffens the fabric and makes it uncomfortable. To ensure the hat’s comfort, we utilized 100% cotton yarn with a 30/3 English Cotton Count (177/3 Denier) as the foundation for the entire hat structure, as illustrated in beige colour in Figure 1. In addition, we applied the thermochromic yarn just to the headband area knitted in a rib structure, as shown in purple in Figure 1. The rib structure was implemented on the headband to optimize its elasticity and smoothness. A plating method was employed to guarantee that only the cotton yarn came into direct touch with the skin. This function helps mitigate skin irritation from the thermochromic coating, especially when developing items for young children.

The hat operates on the idea that when the body experiences a high temperature, the headband of the hat changes colour as a means of detecting the fever. According to Herzog and Coyne [23], fever is defined as a temperature equal to or higher than 38.0 °C for newborns under 30 days old, equal to or higher than 38.1 °C for infants who are 1 month old, and equal to or higher than 38.2 °C for infants who are 2 months old. The thermochromic yarn is customized to change colour from purple to white when the temperature reaches 37 °C, considering the temperature difference between the inner and outer sides of the knitted fabric.

Only headbands were knitted for testing purposes in the simulated body temperature settings, as discussed in the following sections, to simplify the operating procedure. Considering that consumers value both comfort and aesthetic aspects, which can significantly impact the performance of colour changes, various combinations of colours, rib structures, and stretch ratios were used to create the knitted samples. The thermochromic yarns remain purple at low temperatures, but we altered the colours of the cotton yarns as follows: (1) white, which is a commonly used colour and also the colour that the purple turns into when it reaches the threshold temperature, (2) black, which is a commonly used colour and also the complementary colour of the colour that the purple turns into when it reaches the threshold temperature, (3) lime, which represents the complementary colour of purple, and (4) purple, which represents an analogous colour. The fifth colour option supplemented the cotton yarn with thermochromic yarn, representing the scenario when just thermochromic yarn was utilized on the headband.

Three rib knitting structures were evaluated: the 1 × 1 rib, 1 × 2 rib, and 1 × 3 rib. Two stretch ratios, namely 0.6 and 0.8, were tested. The stretch ratio refers to the ratio of the length of fabric to the distance it stretches to fit. For instance, if we assume that the headband is meant to fit a head with a circumference of 20 cm, a headband with a stretch ratio of 0.8 would have a length of 16 cm when no stretching is applied. A smaller headband ratio corresponds to a greater distance that the band needs to be stretched and a higher amount of stress that needs to be exerted on the head in order for it to fit; in other words, it needs to be tighter and could be less comfortable. There are a total of 30 possible sample combinations for testing.

2.2. Body Temperature Simulation and Colour Measurement

An identified gap in the literature is the limitation of research that tests the performance of thermochromic materials in the setting of body fever temperature, ranging from 38.0 °C to 38.2 °C for young children, depending on their days since birth [18,23]. In order to address this issue, we created an experimental environment that mimics the forehead’s temperature (illustrated in Figure 2). A beaker was placed on a heating plate equipped with a temperature-control thermal probe. The beaker was filled with glycerine to replicate the composition of body fluids. A thermal probe was linked to the heating plate to monitor the temperature of the liquid and assist in regulating and sustaining its temperature. The researcher can adjust the heating temperature to any desired value, from room temperature above 100 °C, with an accuracy of 1 °C.

In this project, the heating plate was adjusted to raise the temperature of the liquid from 34 °C to 40 °C, increased by one degree at a time. This was intended to replicate the temperature of the human body in low, regular, and fever statuses. The environmental temperature was regulated to maintain a precise range of 23 ± 0.5 °C, while the humidity level was maintained at 65 ± 5%. A white paper was used to cover the beaker, ensuring a uniform and opaque backdrop colour (as illustrated in Figure 2). The entire set was enclosed within a box and subjected to uniform illumination and reflection from the surrounding lights.

As previously stated, the testing samples were knitted in headband shapes rather than complete hat shapes. The band measured approximately 4 inches in width and 15 inches in length. While the dimensions of the knitted samples varied among different knitting structures, this difference should not influence the assessment of colour change performance. All samples were knitted on a 14-gauge Shima Seiki SSR112 machine (manufactured in Japan). When recording colour differences, Potuck et al. [17] assessed the variation in colour perception by observing visual discrepancies. Other researchers examined colour variations by analysing the spectrum of reflected light [13,24]. This study examined both visual differences and spectrum changes for performance comparison.

During the testing process, a band was placed around the beaker and secured with clips to ensure the desired stretch ratio. After being set, the band’s colour was first measured at room temperature using Xrite’s i1 spectrophotometer at ten locations around the beaker. Subsequently, the liquid in the beaker was heated until it reached the seven specific temperature measurement points. Colours were measured roughly at the same ten measurement locations around the beaker at each measurement point. The thermochromic yarn exhibited rapid responsiveness to changes in temperature, displaying a colour transformation in less than 10 seconds. Nevertheless, to control the liquid temperature’s stability, the researchers ensured that the temperature displayed on the heating plate remained constant at the predetermined setting for at least one minute before taking colour measurements. Each testing sample generated a total of 70 data points.

The gathered data were then examined to determine which combination yielded the most favourable outcomes in terms of the steepness of the colour variations. The spectrum readings of the ten measured locations were averaged before being plotted for comparison. Photo images were captured at room temperature (23 °C) and fever temperature (40 °C) for all samples using a Canon EOS Rebel SL3 camera (manufactured in Japan) in the automatic focus setting. The spectrum and photo comparison outcomes were utilized to address RQ1.

2.3. Consumer Survey

Another gap identified in the literature is the dearth of consumer research on functional and smart textiles, particularly the absence of studies on newly developed products [20]. To fill this research gap, we conducted a consumer study to gauge the response of potential buyers, who are parents of young children, towards the product prototype and gathered their valuable comments. A survey was designed and distributed through Qualtrics. The survey included a Likert scale and open-ended questions (

Table 1. Survey questions for evaluating parents’ perceptions of the product.

Question Category	Label	Question Content
Filter	1a	Number of child(ren).
	1b	Do you have any children currently younger than three years old?
Preference	2a	7-level Likert scale: Unappealing (1) vs. Appealing (7)
	2b	7-level Likert scale: Bad (1) vs. Good (7)
	2c	7-level Likert scale: Unfavourable (1) vs. Favourable (7)
	2d	7-level Likert scale: Not useful (1) vs. useful (7)
	2e	7-level Likert scale: Low purchase interest (1) vs. High purchase interest (7)
Feedback	3a	What are your concerns regarding this newly developed product?
	3b	What are your suggestions to the developer?
Demographic	4a	Year of birth.
	4b	What is the highest level of school you have received?
	4c	Choose one or more races that you consider yourself to be.
	4d	Household income in (previous year) before taxes.
	4e	What is your sex?

). Filter questions were added to ensure the participants were parents of children aged three or younger, and validation questions confirmed that the participants were paying attention when responding. Of 3155 attempted responses, 267 were valid. Descriptive statistics were used to study the participants’ responses to the demographic and Likert scale questions. The text responses to the open-ended questions were first cleaned [25] and then analysed based on the frequency of a word and the co-occurrence of two words to identify the formed topics. The descriptive statistics and text analysis results were used to answer research question RQ2.

3. Results and Discussion

3.1. RQ1: Applicability and Performance of the Product Idea

Figure 3 and Figure 4 display the spectrum readings of various testing samples at seven distinct temperature settings for two fabric stretch ratios: 0.6 and 0.8. Each subplot illustrates a sample’s colour alteration as it was exposed to seven different temperatures that ranged from 34 °C to 40 °C with a one-degree increment. A greater interline spacing in a subplot indicates a more significant contrast in colour between the identical samples under two distinct temperatures. Figure 5 provides a visual comparison of images taken at room temperature (23 °C) and fever temperature (40 °C) for different samples. The data for the self-plated thermochromic sample in a 0.6 stretch ratio was not obtainable due to the fabric structure being too tight to be stretched to match the size of the beaker.

Both the spectrum and visual comparison plots demonstrate that the thermochromic yarn is capable of detecting and indicating changes in the simulated body temperature under specific design configurations.

3.1.1. Performance Comparison of Different Stretch Ratios

Figure 3 exhibits a greater spacing between lines compared to Figure 4, suggesting that a stretch ratio of 0.6 outperformed 0.8. This is because the thermochromic yarn was plated to the cotton yarn, and it becomes visible on the reverse side of a front knit loop. When used in a rib structure, the thermochromic yarn is concealed within the fold between two columns of the front knits. On the one hand, a decreased stretch ratio increases stress distance, creating more room between the front columns and allowing for greater visibility of the thermochromic yarn. On the other hand, the fabric’s thickness results in a temperature differential between the top and bottom of the fabric. When there is more stretch, the fabric becomes thinner. It provides a tighter fit, bringing the thermochromic yarn closer to the surface it measures, allowing for more precise body temperature detection. However, similar to the failure of the self-plated sample in the 0.6 structure ratios, more stretching may result in improved temperature detection but also cause concerns regarding comfort and fit. Hence, achieving an appropriate balance between performance and fit is crucial when choosing the optimal stretch ratio.

3.1.2. Performance Comparison of Different Rib Structures

Three rib structures, 1 × 1, 1 × 2, and 1 × 3, were compared. The numerical sequence in the name of the rib structures denotes the number of knit columns in the front and back sections. For example, 1 × 2 ribs refer to a structural design that consists of one front knit loop column followed by two back knit loop columns, repeated in a regular pattern. The visual comparison diagram (Figure 5) demonstrates that a 1 × 3 rib construction exhibited a more pronounced visual contrast between room and fever temperatures than a 1 × 1 or 1 × 2 rib configuration. The effect was most pronounced in the set of black colour samples.

The visibility of thermochromic yarns on the front side of a fabric can be enhanced by incorporating a greater number of back knit loops in a rib structure. This allows for the presence of a larger area of thermochromic materials, making it easier to observe the colour change of the yarn when the temperature rises. Additionally, it facilitates increased contact between the cotton yarn and the skin, thereby enhancing the comfort of wearing it.

Nevertheless, augmenting the back knitting in the rib structure diminishes the elasticity of the textiles. A rib structure with dimensions of 1 × 2 or 1 × 3 will be adequate for detecting fever in the yarn setting of this research. However, utilizing a 1 × 4 or a structure predominantly composed of the back knit is not recommended, particularly due to the demonstrated failure in stretchability observed in one of the 1 × 3 rib samples. Using the 1 × 1 structure is not recommended either, particularly when the stretch distance is limited. This is because the structure does not allow enough thermochromic yarn to be visible, making it difficult to see the colour difference.

3.1.3. Performance Comparison of Different Colour Combinations

Figure 5 provides a visual representation of the variations in colour combinations, offering guidance on which combinations may be effective. The thermochromic yarn remains purple at low temperatures and transitions to white once the threshold temperature is reached. Figure 5 demonstrates that using white and lime colours for the cotton yarn would be the most effective in accentuating the colour change between room temperature and fever temperatures. Furthermore, these two colours consistently performed well across various stretch ratios and rib structures. Interestingly, white closely resembles the colour that the thermochromic yarns change into when they reach the threshold temperature. In contrast, lime is the complementary colour of the thermochromic yarn at low temperatures. The consistent variation in the spectrum of the white and lime samples depicted in Figure 3 and Figure 4 further supports the efficacy of these two colour selections. The performance of purple and black colour options improved with more fabric stretching and a higher proportion of back knit in the rib structure. However, the colour variations were not as pronounced as those observed in the white and lime colour options.

Since the colour of the thermochromic yarn can be changed, it is advisable for designers to combine the thermochromic yarn with cotton yarn in either the colour that the thermochromic yarn transitions to when reaching the threshold temperature or the complementary colour of the thermochromic yarn at low temperature. The thermochromism in this research refers to the phenomenon of molecular rearrangement, where the pigment typically changes from its original hue to white when exposed to high temperatures. In order to enhance the contrast between high and low-temperature colours on the thermochromic material, it is also recommended to use a darker shade for the thermochromic yarn when the temperature is below the threshold.

3.1.4. Summary of the Answer to RQ1

Regarding RQ1, it is feasible to employ yarn covered with encapsulated thermochromic pigment to produce a knitted hat that can detect fever. Plating thermochromic materials with cotton yarn would enhance the softness and comfort of the product since the rigidity of the materials would be lessened. Nevertheless, various aesthetic configurations would impact the performance of the product. It is recommended that designers refrain from using 1 × 1 rib structures and try to keep a high ratio of back yarn visibility on the front when employing the plating technique. To achieve a noticeable visual difference, it is recommended to use a low stretch ratio and a high stretch distance without affecting the product’s fit. The product is most effective when the colour of the cotton yarn matches either the colour that the thermochromic yarn changes to or the complementary colour of the thermochromic yarn at low temperatures. These tips would assist designers in making intelligent decisions when creating apparel products using thermochromic textiles.

3.2. RQ2: Consumer Perceptions, Concerns, and Suggestions

Out of the 267 valid responses, (1) 99 participants reported having one child, 89 reported having two children, and 79 reported having three or more children. (2) There were 32 participants aged between 20 and 25, 138 aged between 26 and 35, and 97 aged above 35. (3) Out of the total, 33 participants possessed doctoral degrees, 80 held bachelor’s degrees, and 154 had associate degrees or others. (4) A total of 222 participants identified as white, 28 as black or African American, 13 as Native American, 9 as Asian, and 11 as belonging to other racial categories (note: participants could identify with more than one race). (5) Out of the total, 118 participants had an annual household income of less than $60,000 before taxes, 66 participants had a household income beyond $100,000, and 83 participants had a household income range between these two values. (6) Among the participants were 221 women and 46 men.

3.2.1. Perceptions

Figure 6 displays the distribution of participants’ ratings on a 7-level Likert scale for various preference questions. Based on the data shown in Figure 6b–d, it is evident that the majority of participants expressed a positive attitude towards the product concept and believed it would have practical value. This validates the practical worth of the device for utilization among young toddlers. However, around 50% of the participants expressed a lack of appeal to the product, possibly due to the lack of visually appealing features of the prototype. Since the prototype was created in a dull beige hue, it may not appeal to parents who typically purchase vibrant colours for their children. This aligns with the findings of Mcneill and Graham’s [26] research on mothers’ decision-making, which revealed that women were concerned that certain colours, such as black and grey, might not convey the desired message if worn by their children, even though these colours have practical value in connection to their personal fashion. The pairing of beige and purple may optimize the performance. However, it may not be an ideal colour combination for infant products. Additionally, the shape of the cap can be modified to suit the parents’ preferences better. After considering the product’s functional and aesthetic aspects, slightly more than 50% of the participants indicated moderate (5 out of 7) to high (7 out of 7) levels of interest in purchasing. This indicates that such functional textile products have potential in the market. In order to gain a deeper understanding of the specific areas where the product might be enhanced, the text responses to open-ended questions regarding concerns and suggestions were examined.

3.2.2. Concerns

The co-occurrence plots in Figure 7 display words commonly referenced in the responses. The correlation between words emphasizes the occurrence of terms referenced in the same response, thereby facilitating the categorizing of words into topics. In order to enhance the identification of the subjects in the responses that were most closely connected to the question, the plot was captured while highlighting the question’s keyword and its associated words. The keyword “concern” was used for concern-related question 3a, and “make”, as in “make sure”, was used for suggestion-related question 3b. The co-occurrence analysis for question 3-a, “What are your concerns regarding this newly developed product?”, as depicted in Figure 7a, reveals that parents expressed the highest level of concern regarding the accuracy (e.g., “accuracy”, “high”, “false”, and “reading”), safety (e.g., “safe” and “safety”), and usability (e.g., “hot”, “big”, “wear”, “long”, and “time”) of the product.

Most parents expressed scepticism over the product’s accuracy, particularly when it was exposed to fluctuating environmental temperatures, questioning whether the device maintains its level of precision. Additionally, they mentioned the possibility of false positives that would necessitate using a thermometer. They also inquired if the thermometer is washable and remains functional after washing. Parents prioritize safety above everything else when selecting things for their children. While textile items may not be as high of a priority as food when it comes to ensuring safety for young children, some parents have expressed concerns regarding the safety of thermochromic textiles. Parents expressed their concerns regarding the absence of thorough safety testing. For example, parents commented, “My concerns are the product is safe to even go on someone’s head” and “There is a lack of safety testing and results”. Certain parents believe that a hat may not be the optimal choice for utilizing thermochromic yarns due to the fact that some children have an aversion to wearing hats. Additionally, a hat would impede heat radiation while a child is experiencing a fever. For example, parents commented, “The child would not keep it on” and “That it may make them too hot if they already have the fever”.

To summarize, A more suitable medium for young children would be an item that remains with them. Instead of posing a risk to the child, we should discreetly, securely, and comfortably incorporate the necessary features into textile goods. The product should be able to adjust to the specific conditions of the textile product it is integrated into while maintaining its performance during washing cycles and adapting to environmental changes.

3.2.3. Suggestions

The word co-occurrence for question 3-b, “What are your suggestions to the developer?”, as illustrated in Figure 7b, summarized the suggestions provided by parents into two categories: functional values (such as “use,” “soft,” “material,” “comfortable,” “accurate,” “size,” “fabric,” “safe,” and “test”) and aesthetic values (such as “attractive,” “design,” “cuter,” “style,” “fashionable,” and “appeal”). This aligns with the F and A components of the Functional (F), Expressive (E), and Aesthetic (A) Consumer Need Model that has been widely utilized in apparel design [27].

Regarding functional values, parents expressed the need for the product to prioritize safety (e.g., “Maybe something that can’t suffocate a baby”), undergo rigorous testing before being sold (e.g., “Test test test and prove it works and prove it’s safe”), and demonstrate consistent performance across various conditions (e.g., “Make sure it detects fever and not just a hot forehead. I live in South GA and it’s hot here all the time”). These functional features were consistent with the identified concerns in question 3a. Besides, it is also essential to use a lightweight, soft, and comfortable material for the hat. Additionally, it is important to create a product with a long life cycle that can be used throughout the year. Furthermore, proper fit options such as adjustable straps and various sizes for children of different ages should be provided.

Although aesthetics is not explicitly recognized as a primary consideration, parents recommend it to make the product more attractive to a wider range of buyers. Parents desire greater diversity in the product’s kind, colour, and style. For instance, they suggest making the product more appealing by incorporating headbands in various colours and designs (i.e., “I would be more likely to buy if it was a headband and if it was decorated with kid-friendly patterns”). This aligns with the findings obtained from preference question 2a. Besides, several parents proposed incorporating the concept into a sticker instead of a hat due to the sticker’s advantages of affordability, user-friendliness, and entertainment value for children. Although expressive values did not become a prominent subject, a parent proposed inviting more mothers into the product creation process, expressing a desire for their opinions to be considered by the designers.

3.2.4. Summary of the Answer to RQ2

When addressing RQ2, the majority of potential purchasers consider the product concept to be beneficial. However, only a little over 50% of them expressed a desire to purchase the product. This could be because parents thought the product design lacked attractiveness. Most buyers expressed concern regarding the product's safety, accuracy, and usability. They suggested conducting a sufficient number of tests, creating more design alternatives, and carefully considering consumer feedback before marketing the project. The customer survey unveiled both the advantages and disadvantages of the concept. Although there is enthusiasm for utilizing thermochromic textiles for fever detection, a hat may not be a suitable medium for implementing this technology.

The researcher was inspired to investigate alternative places on the body and clothing and accessory categories for the application of thermochromic materials. In recent times, there has been a growing inclination to discuss the efficacy of hats in preventing hypothermia and raising concerns about overheating [28]. The National Institute for Health and Care Excellence recommends using axillary measurements to determine the body temperature of children under the age of five [29]. Bach et al. [30] discovered that back and neck temperatures are the most accurate indicators of typical proximal skin temperatures. Hence, it is recommended that the customers’ perspectives on the concept of fever-detection bodysuits for young children be investigated in the future. These bodysuits would incorporate thermochromic yarns in the back, neck, or axilla regions.

4. Conclusions

A literature review emphasized the necessity of designing textile items with the ability to detect fever in young children, as well as investigating consumers’ opinions about these newly designed products. Hence, this study aimed to explore the application of thermochromic materials for fever monitoring in young children. This was achieved by conducting experiments in a simulated body environment and a consumer study with parents of young children. A knitted hat was developed, including a headband region plated with yarn coated with encapsulated thermochromic pigment. The thermochromic yarns serve as a sensor and indicator for measuring fever on the forehead. Headbands with different stretch ratios, rib structures, and colour combinations were sampled and tested within the simulated body temperature ranging from 34 °C to 40 °C. The experimental findings demonstrated the feasibility of the product concept. It also uncovered optimal configurations for maximizing the hat’s performance. The customer survey results indicated that the parents found the idea intriguing but suggested enhancing the product’s aesthetics, evidence testing, and style variations.

This study provides useful insights into the utilization of thermochromic functional yarn for the purpose of designing goods specifically tailored for young children. The results incorporated recommendations from prospective consumers, which offered valuable insights to improve the design of the product. This study examined the practical use of advanced textiles in healthcare, specifically investigating the product’s viability and its acceptance by consumers. This research helped identify potential economic development possibilities for functional textiles.

5. Limitations and Future Research

Several elements were left out of the experimental design and should be considered for future investigation. For instance, an evaluation of the adhesion of the thermochromic coating was not conducted. While thermochromic materials have been utilized in infant products like spoons and water bottles, it is important to conduct cytotoxicity tests to ensure the safety of these products. Due to the fact the yarn was outsourced, our ability to manage the yarn production process was limited. Further investigations could be directed towards in-house yarn development or collaborating with the supplier’s research team to enhance awareness of the process. While we have observed certain atheistic implications for colour combinations, assessing customer responses to the colour change will be more subjective. Our current body temperature simulation is limited to tests with an accuracy of 1 °C. It would be more advantageous to have the capability to test with a higher accuracy of 0.1 °C and also under varying ambient conditions, mimicking scenarios when young children are wearing the products. The subsequent round of testing should involve establishing collaborations with hospitals and doctors to conduct clinical studies.

6. Patents

A provisional patent, United States Provisional Application No. 63/612,857, was filed for the content in this study.