Coatings which contain two resins which are totally unreactive at room temperature, they are therefore stable in the wet form and may be supplied in a single pack.

Reaction only takes place when the applied coating is heated, or exposed to UV light or some other energy source, a catalyst may be used to promote the reaction or shorten the curing time.

This type of coating was developed mainly for industrial coating of metals and is used for the OE finish on car painting systems, originally in the form of enamels based on alkyd cross-linked with melamine formaldehyde (MF), but more usually nowadays as acrylic with MF and known as thermoset acrylic (TSA).