Cyanate ester is a thermoset material, a polymer that is irreversibly hardened by curing from a soft solid, with a very low glass-transition temperature due in part to its low moisture uptake.
Cyanate esters can be cured and postcured by heating, either alone at elevated temperatures or at lower temperatures in presence of a suitable catalyst. The most common catalysts are transition metal complexes of cobalt, copper, manganese and zinc. The result is a thermoset material with a very high glass-transition temperature (Tg) of up to 400 C, and a very low dielectric constant, providing excellent long term thermal stability at elevated end use temperatures, very good fire, smoke and toxicity performance and specific suitability for printed circuit boards installed in critical electrical devices. A thermosetting polymer, resin, or plastic, often called a thermoset, is a polymer that is irreversibly hardened by curing from a soft solid or viscous liquid prepolymer or resin. This is also due to its low moisture uptake. 
