This is a flux but it really seems to have lost weight have It's liquid and you can hear it when you shake the pen. You must press the tip against the handle and forcefully pull it back to "activate" or open it. I've had more success desoldering with a dab of paste based flux, putting an iron on it, then 4 to 8 leads and then unplugging. With this material it seems quite diluted that I have to suck the solder right out of the felt tip to get the smoke to appear in the vacuum tube. This can be an advantage when desoldering, so that the filters do not wear out as quickly. However, sometimes it's quite difficult to get liquids into what I'm working on. Even if you try to push the tip down and force it to retract, it doesn't always retract and get stuck in the pen. do a few more tests, but it evaporates fairly quickly; something that paste doesn't do. Also, never trust flux without cleaning. nothing is really impure. at least not yet and not what I found. Flux can damage the solder mask and also corrode contacts if not removed from the board; and there is always something left over. Always clean your boards.