Epoxy is a generic term for a class of polymers whose molecule is composed of above two epoxide groups. It is a condensation polymer of epichlorohydrin with Bisphenol A or polyol. Because of the chemical activity of epoxy group, various compounds containing active hydrogen can make epoxy’s ring open and cure crosslink it to netted structure. Therefore it is a type of thermosetting resin. Bisphenol a epoxy resin not only has the highest yield but also has the most complete variety. New modified variety are still increasing and quality has been improving.