Epoxies are produced by cross-linking an epoxy resin together with another chemical called ‘hardener’, or reacting the epoxy resin by itself through catalytic homopolymerisation. The most common substances used as hardeners are polyamines, aminoamides or phenolic compounds. The reaction between a resin and a hardener, also known as ‘curing’ process, creates a polymer with strong mechanical properties, great resistance and durability. The resulting epoxy plastic is more commonly referred to as just epoxy or, somewhat confusingly, also as epoxy resin. Depending on the type of reaction used to produce them, cured epoxy resins can have variable molecular chain lengths and purity grades corresponding to various molecular weights. The molecular weight of the resins determines their possible uses.