A hardener is used in combination with a resin. It triggers a chemical reaction in adhesives, which in chemistry is called cross-linking. In these macromolecular chemistry reactions, a large number of individual macromolecules are linked into a three-dimensional network.

The properties of the cross-linked substances change through the cross-linking process. In general, one can observe an increase in hardness, toughness, melting point and a decrease in solubility.

Hardeners are used in various applications, such as in plastics production, the coating industry, mechanical engineering or adhesive technology.

The choice of the appropriate hardener depends on various factors such as the type of resin, the desired curing speed and the application temperature. They can be produced, for example, based on amides, amines, polyisocyanates or peroxides and are available in various forms, such as liquid, pasty or powdery. The selection is made during the adhesive formulation in the laboratory.