In his guide, he details the difference between XPS (expanded polystyrene) and EPS (extruded polystyrene) and how each product’s closed cell and open cell nature affects the final board.

The boards are often oriented strand board (OSB), and the foam is either polystyrene foam (EPS), extruded polystyrene foam (XPS), or polyurethane foam. Other materials may also be used including ...