2.1.1. Material Flows and Their Cycles

At the regional level, placing industrial sites within the environmental context reveals that the significant material flows feature two types of cycles (Figure 3), which can be extrapolated to a global (planetary) level. One type of material cycle is the traditional one: extracting resources (primary raw materials) from environmental storage sites, processing them into intermediate materials and further to products, the delivery and use of those products, the generation of waste streams and the disposal of the waste into the environment. The second cycle travels a shorter path, consisting of diverting part of the material flow of waste to the generation of secondary raw materials, which are used to substitute primary raw materials. Of these cycle types, the traditional route is more straightforward and is perceived as economically more favourable. While this may have been the case at the beginning of the industrial age, the increasing waste generation makes the recycling–reuse pattern desirable and viable for key materials such as paper [66], metals [67], and even electronic waste [68].

**Figure 3.** Global material cycles.

One obvious essential feature is that both material flow patterns form closed cycles. In this sense, the major degree of freedom within the material flows network is the split between the recycled and non-recycled fractions of the generated waste.
