Fiberglass reinforced epoxy and will work, although there was at least one report of problems with heat of cure being an issue. Others, that from what I gather have more practical experience, say that this should not be a problem at normal mix ratios and batch sizes.
Polyester resin based "fiberglass" will melt the foam.
Some people get kind of prickly if you just say fiberglass w/o specifying the epoxy resin, as this seems to default to the assumption that the resin is polyester.
I have used epoxy and glass over a blue foam mold for a small project and can confirm that these materials are compatible.
