It is a polymer clay called "Primo" or "Sculpy" (he uses both). Check the link above at PlanetUnreal for photos of his other creation the "Izarian". These are based off of designs from Unreal 2 and the creators have been emailing him about them! I'm just really excited for this guy!

You can email him at [email protected] or http://www.sgtskinner.com for info on the guy (again, he is a good buddy of mine).