Thermoset plastics are based on cross linked polymers. This will allow thermoset plastics to be used for higher temperature applications as they do not usually exhibit a melting range and will instead char and burn. Thermoset foams are also generally more resistant to solvents and chemicals.

The most common thermoset foam on the market is polyisocyanurate. While traditional polyurethane foams were created by reacting isocyanate with polyol (and other blowing agents, catalysts, and surfactants) polyisocyanurate foams can theoretically be created with no polyol, using only isocyanate reacting with itself (and other blowing agents, catalysts, and surfactants). In general though, commercial polyisocyanurate foam used in the market is really polyurethane foam modified with polyisocyanurate or a "blend" of the two foams. The use of the blend increases the fire resistance while maintaining the thermal resistance and strength of the material.