Animation showing the formation of a long chain of the plastic polythene from molecules of ethene. Polythene or polyethene or polyethylene is the most commonly produced plastic. Polythene is produced by the polymerisation of molecules of ethene in the presence of a metal_based catalyst. The double bond linking the two carbon atoms black in ethene is broken, forming a new single bond red between the atoms. Polythene can be produced with a wide variety of chain lengths, side branches and densities, with each having different characteristics and consequently different uses.