In fitness and rehabilitation products, material design has a direct effect on performance, comfort, durability, hygiene, and long-term user trust. A resistance band that stretches unevenly, a grip that becomes slippery, or a flexible component that tears too early can quickly lead to complaints, returns, and lower confidence in the product. The key challenge is not simply choosing an elastic material. It is selecting and validating a material system that can perform consistently under repeated stretching, skin contact, sweat exposure, and ongoing mechanical stress.