Polyurethane is a substance categorized as a polymer based on its chemical structure. One manufacturers polyurethane by combining a diisocyanate and a diol, two monomers, through a chemical reaction. This makes a basic material whose variations can be stretched, smashed, or scratched, and remain fairly indestructible. Depending on the different diisocyanates and diol or polyol constituents, the resulting polyurethane might take a liquid, foam, or solid form, each with advantages and limitations.

Some polyurethane is categorized as an elastomer. It has elastic properties while maintaining some rigidity, such as in the wheels of a dolly that absorb shock but don't compress too much. It can be extremely flexible when used as a foam insulator in construction or a foam cushion in upholstery. It can be deformed over and over and still maintain its original shape; in other words, it has a structural memory. Elastomers have made our home and work environments warm and comfortable.