One of the biggest pieces of advice I have ever given to people looking for their own heatsink is to first flip the mass of metal over and look at the bottom. A good surface finish is what we hope to see, and most of the time we'll find something a less appealing. This isn't always the be all and end of a heatsink, though it does tend to knock many coolers out of the performance circle. So why is the surface finish on the bottom of a heatsink so important? The answer to that question lies in something called thermal contact resistance. This is described as the temperature drop across the interface between a composite system. Given a perfectly flat metal base, the degree of thermal contact resistance which exists will depend largely on surface roughness effects.