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.

After your waterproofing has dried, install 2-in. extruded polystyrene (XPS) foam board insulation. Be sure you use XPS—other types of foam board are not as moisture resistant. Stick the foam ...