Dow Blue Foam ("Styrofoam") and Owens-Corning Pink Foam (Foamular) are extruded polystyrene (XPS). XPS is a closed-cell polystyrene foam that is not porous (made light by injecting a blowing agent during polystyrene extrusion, that causes small bubbles to form in the polystyrene as it comes out of the extrusion die) and therefore does not absorb water. Resin does not adhere well because the foam is not porous (less surface area for bonding because there are no connecting passages, open spaces, between cells) and some gas is released from the cells when they are ruptured. Some surfboard builders claim good success glassing XPS after the shaped core (final) is scored/roughed with 20-50 grit sandpaper (IMO the lower grit would be better).