A thermosetting plastic is a polymer that irreversibly becomes rigid when heated. Such a material is also known as a thermoset or thermosetting polymer. Initially, the polymer is a liquid or soft solid. Heat provides energy for chemical reactions that increase the cross-linking between polymer chains, curing the plastic. The rate of curing may be increasing in many cases by increasing pressure or by adding a catalyst.

Examples

Many common plastics are thermosets. They include:

• Vulcanized rubber
• Fiberglass (a fiber-reinforced polymer composite)
• Polyester resin
• Polyurethane
• Melamine
• Bakelite
• Silicone resin
• Epoxy resin