This can be anything from an old sheet to ... Spray painting the faux rocks with a product like Rust-Oleum Stone Creations Spray can add additional texture to the foam to enhance its appearance.

Industrial designer [Eric Strebel] has access to big, walk-in spray booths ... The booth is built from a single 40″ x 60″ sheet of 1/2″ foam core board, a furnace filter, and a vent fan ...