ORIGINAL: Don Pruitt
I use ½ in. Gypsum board. I think this is the correct name. It is a material that looks like a cardboard type material but is compressed down so that it is fairly dense. I think that it is used for insulation. It comes in a 4X8 sheet from Lowe’s for about $13. In it’s original form it is a bit dusty so I paint it with a coat of latex to seal it.
Don - that's Builder's Board. Gypsum is drywall.