Elite Bastards posted a review on the Sapphire Radeon HD 3870 Atomic

In essence, Vapour Chamber Technology is very similar to the heatpipe technology we've seen plenty of times before, taking heat and transferring it away from its source to a cooler area. However, with a VCT cooler this is achieved by providing a vacuum chamber, the inside walls of which are lined with the wick you can see above (the vapourisation wick), which is saturating with a liquid (pure water in this case). As heat is applied to an area, the fluid within it then vapourises and moves to fill the vacuum inside the chamber until it hits a cooler surface (the condensation wick), upon which it will condense, releasing the heat it has taken in during the vapourisation in the process. Once this heat is dissipated, the condensed liquid will return to the heat source via a capillary action (via the transportation wick), at which point the cycle repeats ad infinitum to continually draw heat away from its source, thus acting as a cooling solution.

Sapphire Radeon HD 3870 Atomic Review