It's ACC, with the mass backing on it, and 1/4" padding over the curved parts, but NOT the vertical parts, of the wheel wells. The mass backing makes it fit decent, and the pad helps, too. Its still not a real good fit, in my opinion. I dread carpeting these things...none of the kits I have put in fit to suit me very well. The front piece of this one fits better than any I have used, but it's still not perfect around the tunnel area. At least it was wide enough to come to both door sill plates at the same time...and the heel pad is almost straight and isn't halfway up the tunnel!