It's very unique. It's a little plastic/rubber container, that contains a bunch of little (and I mean little..) beads. That's right, beads. Like tiny little ball bearings. I guess the idea is that they absorb some level of shock.
I don't know if it works. But that's the best description I can come up with. Little beads, that 'counter' the vibration that it encounters.
I personally don't use it. Not that I don't like it.. it's probably perfectly good. I just have an open string pattern stick (POG mid) so the issue of the dampener flying out of the strings is just a deal breaker for me.