Elmer's 900802 Polystyrene Foam Board, 20 x 30, White Surface and Core (Case of 10) Foam board with one color throughout has a 3/16" polystyrene CFC-free core. Smooth surface accepts screen printing, glue, paint or markers. Polystyrene CFC-free 3/16" core. Strong, lightweight and rigid. Cuts cleanly with an X-ACTO knife (sold separately).