I’m looking forward to the result.
If you want to know the density of your foam, put some sheets on a scale, measure the dimensions, divide the weight by the dimensions and there you go. I did it several times for the cheap foam from the hardware store. EPS all is around 12kg/m3 (~1lb foam). XPS varies more from store to store, I guess your XPS will be around 25kg/m3.
These are some foam specs for XPS available in the U.S.
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)
http://building.dow.com/na/en/products/insulation/squareedge.htm
STYROFOAM™ Brand Square Edge Insulation (U.S. Only)
STYROFOAM™ Brand Residential Sheathing (RS) -- 15 psi (1.3 pcf)
http://building.dow.com/na/en/products/insulation/ressheathing.htm
Dow Blue Foam Densities (Dow Building & Construction Answer Center)
http://dow-styrofoam.custhelp.com/app/answers/detail/a_id/665/~/what-are...
Owens-Corning "Pink Foam" (XPS also):
Foamular 1000 -- 100 psi, 3.0 pcf density
http://www.foamular.com/assets/0/144/172/174/bf64ec70-16f1-4748-abc7-c9d...
Foamular 600 -- 60 psi, 2.2 pcf density
http://www.foamular.com/assets/0/144/172/174/bf64ec70-16f1-4748-abc7-c9d...
Foamular 400 -- 40 psi, 1.8 pcf density
http://www.foamular.com/assets/0/144/172/174/bf64ec70-16f1-4748-abc7-c9d...
Foamular 250 -- 25 psi, 1.55 pcf density
http://commercial.owenscorning.com/assets/0/144/172/174/11b5f50a-0f80-4f...
Foamular 150 -- 15 psi, 1.3 pcf
http://commercial.owenscorning.com/assets/0/144/172/174/1b241d3e-6d7f-4c...
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.
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 often used for surfboard cores.
Read the following link for a good discussion about EPS and a brief discussion of XPS foams:
Thanks for the help. I found a local source for the Owens-Corning Foamular XPS, both the 400 and 600. I’m planning on shaping a Simmons-inspired SUP (a la King Paddle). I’m looking to go 8’ x 30" x 4" for a volume of approximately 120 litres. I’ll use keels and keep it flat.
I’ve notice that the noses of most of the mini-simmons posted here look like hulls. The boards on the Hydrodynamica site all have the “hulled” front end, too. I’ve never tried shaping a hull. Any pointers would be appreciated.