The most common polymer additives are stabilizers, plasticizers, lubricants and flame retardants. Stabilizers are added to prolong the useful life of a polymer formulation by protecting it from thermal and light-assisted oxidation. This process is caused by the formation in the polymer chain of free radical sites which can react with oxygen to form unstable peroxy radicals and ultimately cause polymer chain scission. Stabilizers are divided into four main classes: UV absorbers, primary antioxidants, secondary antioxidants and quenchers.