I don't believe the blue (or pink) insulation foam is porous. In any case, I use Murphy's Soap as a mold release, just wipe the surface of the blue mold and you should be okay
The blue insulation foam has a protective plastic film that would keep it from being porous, but even if it was removed, the foam has a tight smooth surface. I use it with concrete and have to rough up the surface a bit to get the concrete to adhere to it.
I'm actually using the foam as the model and casting a plaster mold from it. Sorry if I wasn't clear about that. I carved half a vase from the blue foam and sanded it a little to smooth off the uneven parts, so the foam no longer has the plastic film or that nice, smooth surface that the original outside surfaces have when you get it.