Gruntville posted a review on the Noctua NH Series Heatsinks

Noctua, a recent up start in Austria, has entered the market with two, high performance cooling solutions; the NH-U9 and NH-U12. Both heatsinks utilize 4 dual heat-pipes joined to a copper base and attached to aluminum fins to disperse heat. The only difference between the two units is size; with the NH-U9 accepting 80 and 92mm fans while the larger NH-U12 is designed for use with 120mm fans. While heatpipe technology is nothing new to the cooling industry, the NH-U12 does look to have some of the longest running copper heatpipes I've seen to date. Due to their massive size, both heatsinks can operate without the aide of an attached fan but are capable of utilizing up to two fans for maximum cooling.

Noctua NH Series Heatsinks Review