Before PVC can be made into products, it has to be mixed with a range of additives. The essential additives for all PVC materials are heat stabilizers and lubricants. In the case of flexible PVC, plasticizers are also the main additives. Other additives, which may be used, include fillers, processing aids, impact modifiers and pigments. Additives will influence or determine the mechanical properties, light and thermal stability, color, clarity and electrical properties of the product. Once the additives have been selected, they are mixed with the polymer in a process called compounding