Tested polyester resin on the common pink rigid styrene foam and also polyisocyanurate foam. Both available at the home centers. Polyester resin melts styrene foam, but not polyisocyanurate foam. Polyisocyanurate foam is what surf boards and boats are made from. The difference between what I tested from the home center and what you buy for surf boards is the density. Surfboards are typically about 5lbs density foam, the stuff from the home center is 1 or 2 lbs. A huge difference in price too. Using the 1" thick home center version will cost about $60, the 5lbs stuff about $400 plus. We'll see how well it works.

I tried pealing off the cured resin from the foam, and it pulled the foam apart, so the resin does adhear, the foam is just not very strong.