Bit Tech published a group test of five heatsinks from Asus, Scythe and Zerotherm:
The BTF90’s performance was somewhat surprising, as it managed to take the top spot for CPU temperatures. The use of copper throughout the heatsink has obviously paid off but it would have been good to see the cooler deliver the same performance with lower noise at full load.
Copper’s thermal conduction is better than aluminium’s, but its thermal radiation is worse than aluminium (meaning that it tends to be more reluctant at letting heat escape). As a result of this, the BTF90 responds better at higher fan speeds than some of the hybrid heatsinks this goes up against and therefore we can understand why Zerotherm has opted to increase the speed as temperatures increase.
Its results were better than the Zalman CNPS9700LED with both coolers running at high speed, but neither is really suited for a near-silent system. Thankfully, the BTF90 is quieter than the CNPS9700LED, but it’s still the loudest cooler at load in this selection of heatsinks."