What's inside the world's fastest heat conductor?

The Action Lab Man compared the heat transfer speed of a heat pipe with a similar looking copper rod. The heat pipe transfered heat two orders of magnitude faster than the pure copper. What's inside the heat pipe? The Action Lab Man cut it open and discovered that the heat pipe was a hollow copper pipe with a spongy copper inner wall. The pipe has a bit of water in it, which wicks into the spongy copper surface. The interior of the pipe is under very low pressure. When the pipe is heated on one end, the water very quickly vaporizes (water boils at room temperature in a vacuum) and moves rapidly to the other side, where the pressure is lower.

Image: YouTube