Shield making materials?

I'm (attempting) to make myself a shield that's as light as possible, so I thought I'd give foam a try before I go the plywood route (also that way I can easily carve out space for my hand and make it a punch shield). There's a hard foam I'm looking for that I'm almost sure I've seen people use in the past. I THINK it can be harvested from particularly cheap boogie boards, but as its not boogie board season are there any other sources anyone can think of? Or other materials they'd recommend?

Try the foam sleds with the plastic bottoms.  There are round ones that work well, that is what shane helped me make mine out if and it is amazingly light.

Also, the Pink/Blue/Green insulation foam.  It's usually about 2" thick, and sold in sheets 4 feet wide or more.  It can very easily be carved with a razor blade.  A little more difficult to make a punch shield out of it, but I know it can be done.  Frank uses one made by Tom S.

His was exactly the shield I had in mind. awesome, thanks