Polyurethane does not have a melting point because it is a thermosetting polymer, so when it is made, it becomes irreversibly hard. When exposed to extreme heat, polyurethane ignites and burns.
Because polyurethane is combustible if exposed to sufficient heat, its use is regulated by the fire codes and building codes of local and state governments. Following fire safety standards is important when dealing with polyurethane building materials and furnishings. When items with polyurethane content burn, they produce toxic smoke composed mainly of carbon monoxide, and the smoke also contains hydrogen cyanide and nitrogen oxides.
Polyurethane was first developed during World War II as a replacement for rubber. After the war, research continued to make it more commercially available. It is a plastic material made by combining a polyol, an alcohol with multiple hydroxyl groups, with a di-isocyanate or a polyisocyanate along with specific additives and catalysts. Because various polyols and polyisocyanates can be combined, a wide range of materials can be made, such as various types of foams, sealants, coatings, adhesives and moldings. These are used in the production of many products, including clothes, foam in appliances, automotive parts, carpet padding, foam cores for walls and doors, roofing material, composite wood, electronics, furniture, mattresses, sealant for boat hulls, tubing for medical devices and packaging.