[Otto]

Originally Posted by California98Civic

Gonna be revealing more of what I don't know here...

By "pink board" we mean something like this? INSULPINK Foam Insulation Board - Residential Insulation - Owens Corning



Will the resin dissolve the styrene even if the styrene is encased in polyurethane foam first?

Not if the polyester resin does not contact the polystyrene. There are barrier or prophylactic methods to protect polystyrene, so google for foam sculpting websites for hobbyists and artists. Could be, just use Gorilla Glue (polyurethane glue) to bond the two types of foam together.

Or, even though epoxy is more expensive than polyester resin, you're not using that much of it, so cost difference is insignificant. Or, maybe there's an offset in cost of polystyrene vs. polyurethane foams, such that the bottom line cost difference for the project is no big deal.

I don't know where vinylester resin fits in all this discussion about chemical compatibility with polystyrene or polyurethane foams, but am reasonably certain that at typical homebuilt curing temperatures, vinylester resin is essentially as strong as epoxy, but much less expensive. Could be, vinylester resin is a good cost/benefit compromise for use with both types of foams.