I used this between a 100W LED and its fan-cooled heatsink. I don't have any objective heat measurement on this assembly, but I can say that the results made me think I didn't need anywhere near as big a heatsink -- instead of one sized to fit a 120mm fan, I could probably be using one sized to fit a 40mm fan. Seems to be good stuff, and even though the tube is very small, a little goes a long way.