Exactly what I’m looking for. I want to know about all the options others have tried before I decide how I’m going to make the first XPS blank. Thanks!
For reference, so we are all working from the same page. Here is the information I have picked up about XPS foams over the past few years:
psi = pounds per square inch (compressive strength)
pcf = pounds per cubic foot (density)
Dow “Blue Foam” (XPS):
STYROFOAM™ High Load 100 – 100 psi min. compressive strength (density, 3.0 pcf)
STYROFOAM™ High Load 60 = 60 psi min. compressive strength (density, 2.2 pcf)
STYROFOAM™ High Load 40 – 40 psi min. compressive strength (density, 1.8 pcf)
STYROFOAM™ Brand Square Edge Insulation – 25 psi (density, 1.6 pcf)
STYROFOAM™ Brand Square Edge Insulation (U.S. Only)
STYROFOAM™ Brand Residential Sheathing (RS) – 15 psi (1.3 pcf)
Dow Blue Foam Densities (Dow Building & Construction Answer Center)
Owens-Corning “Pink Foam” (XPS also):
Foamular 1000 – 100 psi, 3.0 pcf density
Foamular 600 – 60 psi, 2.2 pcf density
Foamular 400 – 40 psi, 1.8 pcf density
Foamular 250 – 25 psi, 1.55 pcf density
Foamular 150 – 15 psi, 1.3 pcf
XPS & EPS Foams
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).
EPS foam is expanded polystyrene. EPS is made by heat fusing polystyrene beads. There are air spaces between beads, which means it will soak up water, but epoxy resin bonds well to it in the 2.0-2.5 pcf densities. It can be found in 1.0-3.0 pcf densities. The 2.0-2.5 pcf densities are commonly used for surfboard cores.
Read the following link for a good discussion about EPS and a brief discussion of XPS foams: