Polystyrene foam dissolves in uncured polyester resin, so the obvious, cheap thing does not work. Polystyrene foam does not dissolve in uncured epoxy glue, and I suspect that polyurethane foam might not dissolve in either uncured polyester resin or epoxy resin.
1. Does anyone know for sure which foams are compatible with which resins? 2. Where can I get epoxy resin which cures rigid, like polyester resin does? I've unsuccessfully tried epoxy glues -- not rigid enough. In the late 1960's, I tried some epoxy resin which was designed to be used with fiberglass, but it cured to a solid which was noticably more flexible than polyester resin. 3. Bodies, wings, etc. of some kit airplanes are made by covering foam forms with epoxy reinforced with fiberglass or carbon fiber. What kind of foam? What kind of epoxy? 4. Open-cell foam would soak up resin and become heavy. Where can I get closed-cell foam? How do I cut it so I don't open up the cells near the surface?
-- Gerry