Is polyurethane a rubber or a plastic?

Polyurethane is technically classified as a plastic, specifically a polymer, but it is a unique plastic that can behave like both plastic and rubber depending on its formulation. Chemically, polyurethane is a polymer made by reacting diisocyanates with polyols, and it belongs to the family of plastics, not natural rubber. However, polyurethane is often called an elastomer because it can be made to be flexible, stretchy, and resilient like rubber. In its hard form, such as in wood finishes, hard foams, and rigid insulation, it acts like a hard plastic that is tough and protective. In its soft form, such as in flexible foams for mattresses, spandex fibers, soft wheels, and faux leather, it acts like rubber, being elastic, bouncy, and abrasion resistant. So while it is chemically a plastic, functionally it can be a rubber substitute and is often described as a rubber-like plastic or elastomeric plastic. Industry classifications list polyurethane under plastics and under elastomers. Unlike natural rubber from latex, polyurethane is synthetic. So the most accurate answer is that polyurethane is a plastic that can be engineered to have rubber-like properties, making it a bridge between plastic and rubber.