It's probably electronics grade silicone, similar to caulk minus the corrosive curing agent. It's not bad for potting and, for practical purposes, not too bad for heatsinking flashlight LEDs either. Consider that most LED flashlights need to be upgraded after 3-4 years anyway and I don't think upgrading from Fujik to a more "premium" thermal compound is worth it. The performance gained by upgrading to easy-to-find "premium" compounds like Arctic Silver aren't that dramatic. And the really good stuff is hard to find and is prohibitively expensive. Fujik, for budget lights and if it is applied correctly, is not a bad choice.