Shoe insoles are predominantly made from expanded foam sheets – usually polyurethane, or PU for short. Unfortunately, these thermally deformed materials have very limited resistance to water, heat, light, and sweat. Due to the conditions inside the shoe, such as the warm, humid climate and mechanical stress, the increasing abrasion of the foam material is unavoidable. Furthermore, these insole materials age rapidly and lose their mechanical durability after just a few weeks.