Thermosets are plastics that closely cross-link when heated. This cross-linking chemically takes place between the molecules of the starting materials as an irreversible process, i.e. as soon as such a material is cross-linked, it can only be processed mechanically. Thermosets are mostly hard and brittle.
Since Thermosets do not soften under renewed exposure to heat, they are often used for electrical installations. The Thermoset cluster also includes polyester, polyurethane resins in varnishes and surface coatings and more or less all synthetic resins such as epoxid resins.
There is no general evaluation of Thermosets just like with Thermoplastics. For example, a phenolic resin filled with wood flour has a different characteristic profile than a polyester filled with glass fibre.