As most of today's PC enthusiasts use high-viscosity thermal compounds, the contact surface of Noctua coolers is optimised for use with this type of paste. The micro-grooves at the contact surface ensure that high-viscosity thermal compounds are dispersed to a uniform thin layer across the whole contact area and that no air pockets remain between the cooler and the CPU.
With a polished, mirror like surface, the risk of uneven dispersion is much higher. As too thick layers of thermal paste and air pockets drastically deteriorate heat transmission, the micro-grooves are of vital importance to the overall cooling performance of Noctua coolers when used with today's high-viscosity thermal pastes.
As the Integrated Heat Spreaders (IHS) of today’s CPUs are slightly concave, the cooler’s contact surface has been deliberately designed to be slightly convex in order to ensure optimal contact. This way, more contact pressure will be applied at the centre of the IHS directly above the DIE, which results in better heat transfer and improved overall performance.