Epoxy resins are a family of synthetic resins, including products, which range from viscous liquids to high-melting solids. The resin molecule contains as reactive sites one or more oxirane or epoxy groups, usually in the form of a glycidyl group. The most commercially important resin is the glycidyl ether of bisphenol A, produced by the condensation of epichlorohydrin and diphenylpropane (bisphenol A). Epoxy resins with different characteristics are also produced commercially by reacting epichlorohydrin with other materials. To be of use, the resins must be crosslinked with a curing agent or hardener. The choice of curing agent is of importance in designing an epoxy resin system for a given application. The major reactive groups in the resin, the epoxy and the hydroxyl groups, react with many other groups so that many types of chemical substance can be used as curing agents. These include acid anhydrides, aliphatic and aromatic amines and polyaminoamides. Some curing agents will crosslink the resin at ambient temperatures while others require the application of heat. This International Standard provides an overview of the ISO test methods used to characterize epoxy resins. The listed property to be determined in any given case depends on agreement between the supplier and customer.