Final answer:
Hair is the nonliving material mainly made of keratin and has various functions including protection against UV radiation and acting as insulation.
Step-by-step explanation:
The nonliving material primarily composed of keratin is hair. Hair is a characteristic feature of mammals, consisting mainly of keratin-producing keratinocytes. It starts growing from a follicle in the dermis and by the time it reaches the surface, the hair is mainly composed of dead cells filled with keratin. Hair has several homeostatic functions, such as insulation, protecting the skin from UV radiation, and acting as a sensory input.