Plastic pipe with insulation. The red pipe, and the black mantle are made of polyethylene, the yellow-brown foam is made of polyurethane

Polyurethane is a polymer. Its name is often shortened to PU or PUR. Polyurethane is made of organic units, which are joined by urethane. Polyurethane polymers are formed through step-growth polymerization. In this process, a monomer containing at least two isocyanate functional groups reacts with another monomer containing at least two hydroxyl (alcohol) groups in the presence of a catalyst.

Polyurethane is available with different levels of stiffness, hardness or densities. Examples for such materials are:

• Low-density flexible foam used in upholstery
• Low-density rigid foam used for thermal insulation and RTM cores
• Soft solid elastomers used for gel pads and print rollers
• Low density elastomers used in footwear
• Hard solid plastics used as electronic instrument bezels and structural parts