Originally Posted by Ravens Nest
And here's a quote off there site on what thermal compound is..
Due to the machining process used in making heat sinks, just about every heat sink will have a rough surface. To the human eye it may look flat or even feel smooth, but there are microscopic groves in the surface. These groves will trap air between the heat sink and the CPU, and cause a poor transfer of heat. Thermal compounds such as Artic Silver and Nanotherm are used to fill these groves and help transfer the heat from the CPU to the heat sink.