Polyurethane ( PUR and PU ) is a polymer composed of organic units joined by carbamate (urethane) links. While most polyurethanes are thermosetting polymers that do not melt when heated, thermoplastic polyurethanes are also available. Polyurethane polymers are traditionally and most commonly formed by reacting a di- or poly- isocyanate with a polyol . Both the isocyanates and polyols used to make polyurethanes contain, on average, two or more functional groups per molecule. Some noteworthy recent efforts have been dedicated to minimizing the use of isocyanates to synthesize polyurethanes, because the isocyanates raise severe toxicity issues. Non-isocyanate based polyurethanes (NIPUs) have recently been developed as a new class of polyurethane polymers to mitigate health and environmental concerns. [1] [2] [3] [4] [5] Polyurethane products often are simply called “urethanes”, but should not be confused with ethyl carbamate , which is also called urethane. Polyurethanes ne