Open Cell Foam. As I build out my garage climbing wall it becomes cumbersome to move my bouldering pad along with me (especially if I'm out there alone) so I was thinking about getting a couple sheets of foam and just leaving them on the floor full time. The stuff is pretty expensive though, I think I am better served by buying some used bouldering pads on Craigs List, at least then I have additional pads I can take to the crag.