I use the pink foam from Lowes, lay a peice of acetate down, then two layers of fiberglass, dry, then add the resin and get it good and wet and free of bubbles, add a layer of balsa, more glass, more resin, another layer of acetate, then the foam, and as much weight as i ca throw on top. Turns that crappy paperthin brown balsa that bends like paper stiff in no time...
Scott McNeely