Polyurethanes are a class of linear polymers characterized by a molecular backbone that contains carbamate groups (-NHCOO). These groups are also called urethane groups and are the result of a chemical reaction between a diisocyanate with a polyol. First investigated in the late 1930s, polyurethanes have become important materials used for a wide variety of applications from building insulation to athletic apparel.

Research in the chemistry of polyurethane materials was initiated by the German chemist, Friedrich Bayer in 1937. This early work was based on toluene diisocyanate reacted with dihydric alcohols. One of the first crystalline polyurethane fibers was Perlon U. In 1953, commercial production of a flexible polyurethane foam was begun in the United States. This material was used as foam insulation. In 1956, more flexible, less expensive foams were made. In the late 1950s moldable polyurethanes were produced. Also, spandex fibers, polyurethane coatings, and thermoplastic elastomers were introduced.

Polyurethanes have many characteristics that make them useful for a variety of applications. They are produced in four different forms including fibers, elastomers, coatings, and cross-linked foams. Polyurethane fibers are lightweight and have a high degree of stretchability which makes them good for applications like swimsuits and other athletic apparel. The elastomers can be stretched but will eventually return to their original shape. They are resistant to abrasion and grease, and have good hardness. This makes them useful as base materials for small wheels. Polyurethane coatings demonstrate a resistance to solvent degradation and have good impact resistance. These coatings are used on surfaces where these characteristics are important such as bowling alleys and dance floors. Foam polyurethanes have high-impact strength. They are used for the production of pillows and cushions.