Is it 2.5 lb/ft^3 density, or 25 psi? Usually they go by psi. I've been obsessing over foam lately. Typically for structural sandwich applications PVC or PU foam is used ~5 lb/ft^3 density. That stuff is real expensive. So I've looked into Foamular 600 and Dow 60 which are both 60 psi XPS foam (vs the Foamular 150 15 psi stuff at Home Depot). But where I live it isn't sold in stores and it can't be ordered in quantities less than 50 sheets, which is way more than I need.
Even the heavy duty 100psi styrofoam only goes up to 3 lb/ft^3.
http://www.foamular.com/assets/0/144/172/174/98cf58e1-c3d2-4b6c-beb5-2063215bea18.pdf So it's quite a bit lighter than PVC structural foam. Total Composites and Styromax both use XPS foam in sandwich construction, but it is probably the heavier duty stuff.
http://www.styromax.com.au/category/products/#styromax-panels
It's hard to find details on sandwich construction, and there are a lot of people claim that styrofoam doesn't work for structures because it is too weak. Apparently the two manufacturers above disagree. I did find one discussion on a boat forum where it appears they concluded it would work, but you just wouldn't be able to build as strong a panel as with PVC.
http://www.boatdesign.net/forums/fi...uilding/extruded-polystyrene-xps-24213-2.html
Bottom line is we aren't building big boats and pounding them over waves, and styrofoam should be viable for a structural core, just not as good as PVC. I'd use the heaviest you can find though, and test it well.
The minimum is $10k at Total Composites, but the normal additions and shipping add up. I didn't get a quote from them but someone else posted that it was $18k +engineering, +shipping for their truck camper shell.
