Re: Great Stuff Foam
I'm pretty sure great stuff is an expandable polyisocyanurate foam. Normal pourable floatation foam is a polyurethane.
Chemically I'm not sure what the exact differences are, but there will be some with regard to resistance to chemicals.
Great stuff is closed cell, which means it won't sponge up water, just like polyurethane foam.
But, great stuff is far from structural... it's very low density, so if your boat could benefit from extra stiffness, I'd use the polyurethane instead.
Probably the biggest reason not to use it is convenience. Pourable foam costs about $10 a cubic foot at low density, one can of 16 oz. great stuff is something less than a cubic foot (per the great stuff web site, it's a 3/8 to 1/2 inch bead about 335 feet long) which costs about $4-$8 depending where you get it. But you have to sit there holding the trigger on the can for 5 minutes per can to get it all out. Then get it spread into the space you want to fill.
You also can't install it under decks that easily.. if your stringers have no deck on them, it would sort of work.
So while I guess you could use it, there's not much reason to do so unless you already have a couple cases of the stuff lying around, and you don't mind spending a few hours spraying it in.
Erik
