The name of the board is foam-core board. Most craft stores - Michaels, A.C.Moore, Hobby Lobby - carries it. And you can get it at places that do framing. It can be pricey. I know around here the regular price is about $3 a 20x30 sheet. So when I find it on sale of $1, I usually buy 30-40 sheets. I use it alot - signs, making boxes, etc. My husband uses it too.