It's a very thin foam that comes on a roll. It's approximately an 1/8 inch thick and about 36 inches wide. It cushions the floor and separates the flooring from the slab and keeps the concrete from wearing the reverse side of the flooring. Since it is foam it also makes the laminate seem a bit softer to walk on and work on. Carpet pad would not work because it would move way too much and it's too thick. Pergo was the first to use the concept, and that is where the moniker of "a floating floor" came from. Because you glued the tongues of Pergo and never nailed it, you laid the floor on the foam padding and it "floated" above the subfloor or slab.