Thermosetting plastics, also known as thermosets, are plastics that become rigid and nondeformable after hardening. They are one of the three different groups into which polymers can be divided – thermoplastics, elastomers and thermosets – according to thermosetting degree of the macromolecular chains. While thermoplastics have no cross-linking thermosetting points and are therefore fusible, elastomers and thermosets are thermosetting, not fusible, and disintegrate if the decay temperature is exceeded (pyrolysis).
Bakelite, a phenoplastic, was the first thermoset to be industrially produced at the beginning of the twentieth century. Bakelite was invented by Leo Henricus Baekeland a Belgian-American chemist.