First created in 1938 and later used in 1946 epoxy resin based on bisphenol A and epichlorohydrin has evolved in what it is today, used in all sorts of industries and applications. Epoxy resins are low or high molecular weight thermoset polymers.
Today’s epoxy is largely derived from petroleum although some nuts and plants derived sources are now becoming commercially available
Epoxy resin systems usually involve a resin and a curing agent and offer excellent mechanical, physical and chemical properties, if desired, high functionality resin grades are produced for certain applications,  usually the systems are highly viscous and are heated when applied but they can be formulated to obtain specific characteristics in viscosity, curing times, thixotropy, hardness, flexibilty, etc. as with any other epoxy product.
Epoxide content is used to calculate the ratio of hardener for a given formulation by stoichiomety. This is commonly expressed as the epoxy equivalent weight and aims at achieving maximum cured properties.
Epoxy systems can be blended with different types or grades of epoxy, plasticizers, fillers and a great number of additives to create a working formulation that with a curing agent satisfies the specifications and costs of a project or application.