Synthetic oils available today use a combination of up to three different synthetic base fluids, including synthetic esters, polyalphaolefin (PAO) and alkylated aromatics. Whereas conventional oils contain molecules of varying sizes, the molecular structures in synthetics are consistent in mass and shape. This uniformity means those molecules create less friction as they collide, and less friction means less heat. Synthetic oil manufacturers also mix in additives and other liquids such as detergents, dispersants, antioxidants, friction modifiers and anti-wear additives, all in varying amounts to result in an exact blend for specific environmental conditions. Synthetic oil flows better in cold weather, making engine starts easier and offering better protection. In addition, synthetics resist viscosity changes at extremely high temperatures that can break down or evaporate molecules in conventional oil. When this kind of deterioration happens, metal-on-metal contact may occur, causing permanent damage to the engine.