Polyurethane foam refers to a number of different types of foam consisting of polymers made of molecular chains bound together by urethane links. It can be flexible or rigid, but has a low density. Flexible polyurethane foam is most often used in bedding and upholstery, while the more rigid variety is used for thermal insulation and in automobile dashboards.

Flexible polyurethane is made in blocks and then cut to its desired shape. This is the way in which furniture cushions are made, for instance. Some materials can substitute for this application of polyurethane foam, such as polyester fiber or steel springs. However, polyester fiber does not recover nearly as well as foam does after compression. Steel springs recover well, but can become noisy as they get worn out. They also require some form of cushioning between them and the user.

In addition to the flexible and rigid types, semi-flexible polyurethane foam also exists, and is used extensively in automobile interiors. Seats, armrests, and headrests are frequently made from the semi-flexible variety of this material. In the case of seats, the foam is formed in a mold, and then removed and upholstered.

Rigid polyurethane foam has many relevant applications in construction. Many odd and detailed shapes such as sculptures and domed ceilings are far easier to make with foam than with wood. Some manufacturers sell a specialty rigid foam that is used to replace wood in carved signs and three-dimensional topography models. It is also used as home insulation, rigid boat hulls, tennis racket grips, and even surfboards.

Polyurethane foam can also be made into a form that sprays easily and then rapidly expands as it dries. It can be tailored to have many different physical properties, depending on the desired use. In this form it can be used as industrial insulation, and also as a roofing material that is waterproof and long-lasting. It is often applied to boats, ships, and floating docks. In higher-density forms, it has also been used to increase the structural strength of aircraft wings.

Spray polyurethane foam is one of the most versatile building materials in existence. It is also environmentally friendly in that it does not contain or give off any chemicals that are harmful to the environment or to general air quality. Even so, care must be taken when applying the foam, because the fumes that it does give off can be dangerous if not properly ventilated.