To build a high performance lubricant, pure synthetics use high-quality base oils. This is like having an incredibly strong foundation. Thermal conductivity is one characteristic of higher quality base oils. The fluid has a greater capacity to absorb heat, which it can then transfer to a cooler area. As a result, heat can be transferred from high temperature areas, such as the lifter-camshaft interface or the highly loaded connecting rod bearing, to an oil cooler or to the sump, where it can be conducted to cooler outside air.
As a result, synthetic oils operate at a much lower temperature, which means they last longer. Combined with a more refined additive package that also lasts longer, this means that, even though pure synthetic oils are more expensive, their drain intervals can be extended so that over a longer period of time, they are less expensive to use than mineral-based oils.
Synthetics have certain advantages over standard petroleum base oils. They can be thought of as molecules that are designed for ideal performance. Synthetics have higher resistance to heat and oxidation. They have lower pour points, which means they remain liquid at extremely low temperatures when petroleum base oils would become gels.
They also have a higher viscosity index than petroleum base oils, which means that they thin less as they are heated. Due to their purity, they are generally perfectly clear, almost like water. All of these performance characteristics do come at a price of course, but racing oils and other severe applications call for this higher degree of performance.