In scientific terms, polyurethane is a polymeric material containing (-NH-CO-O-) produced by the reaction of polyols with an isocyanate.
Chances are that you are not a scientist, but more likely an engineer, buyer or manufacturer seeking to reduce cost and improve performance in your machinery or products.
Put simply, polyurethanes are materials which offer a dynamic range of properties which can be tailored to an extraordinarilly wide range of applications.
This is not to say that polyurethanes are the universal answer to all design challenges; however, they are often a superior choice to plastic, rubber and steel because they can embody the characteristics of all three. Polyurethanes can be formulated to resist chemicals, water, shearing and tearing, impact, heat and cold, and many other elements that cause traditional parts to wear prematurely and eventually fail.