If simply removing dirt and fingerprints from your CPU cooler is not enough, you can use finest sandpaper. This applies exclusively to copper and aluminum heatsinks. Polishing of the Cooler is SO Important ! There are several reasons. The surface layer of the radiator changes after many years. In principle, to clean the surface layer on the cooler from various impurities, old thermal paste, copper oxidized surface layer, leveling unevenness and so on.