It's Evercoat Polyester putty, sold in automotive stores. It's the best putty I've ever used! It's a 2 part putty that dries in a 1/2 hour, sands very easily, and never shrinks! A bottle of it will last at least 2-3 years(unless you're like me and use it on everything, including the crack in my head!!! ). I swear by the stuff, it works great!