polyurethane

This term refers to a class of polymers used extensively in industrial and domestic applications. In a manufacturing context, it describes the raw synthetic resin used to create flexible foams for mattresses or rigid structural components. In a woodworking or home improvement context, it specifically denotes the clear, protective varnish applied to surfaces. Because it is a chemical substance and a material, it is treated as an uncountable noun and cannot be pluralized; one would refer to a "layer of polyurethane" or "types of polyurethane" rather than "polyurethanes" in standard usage.