[Stan]

Originally Posted by nimblemotors

Good info Stan,
I was at Lowes and saw they had some Polyisocyanurate Foam board,
twice as expensive as EPS foam, but I took a tiny sample home and it didn't melt from polyester resin. It is apparantly a stronger type of polyurethane
from a what little wikipedia says Polyisocyanurate - Wikipedia, the free encyclopedia
Do you know much about this stuff? I'm going to use some of it in my car, but now I'm thinking maybe my sailboat project even though I will use epoxy on the boat, this foam seems a LOT cheaper than PVC foam.

Yes, I'm very familiar with this foam. There are several different formulations of urethane foams and this is one of them. And in fact, is exactly what I had in mind when I wrote under Urethane Foam, "Sold as tan-colored closed-cell insulation at home improvement stores."

The challenge with urethane foams is that at low densities and thin sheets they tend to break down over time into dust (literally) under repeated vibration and pounding loads, so I recommend not using them in boat hulls, homebuilt airplanes, car body parts, etc. You live in Sactown, and pvc foam is available at Interstate Plastics for $70 for a 4'x8'x1/4" sheet.

I realize that may give you a bit of sticker shock, but pvc foam is a MUCH better choice, and in the big scheme of things, isn't much compared to the price of a complete boat.