Question about foam and mold cast making


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I been using clay to sculpt, mold, then resin cast cosplay piece and it fine and all. It just take some "care" for afterward if you get sick of the project to save it till tomorrow. A friend of mine suggested foam like" GREAT STUF" expanding foam to make block out of and carve/sculpted. but im thinking insulting foam sheets them stack them to brick. I have use Styrofoam in the past with little success to make a mold out of. I do know tooling foam works but it expensive.
Can anyone give me there advice or tips with insulting foam or great stuf expanding foam with mold making and craving?
PLease and thanks

What i want to do it make a piece out of foam, smooth it, pour silicone on it in a mold with out it desolving "melting", let it dry and then pull it out of mold, pour resin and make the cast of what i made.

Done this with clay to many time, but foam and great stuf craving, sculpting, dont have a clue
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Most foams, except for tooling foam, are really only going to be good for the core of what you are making. You just won't get it smooth enough on it's own unless that is the texture you are going for. You are going to have to cover the foam with auto body filler or something else you can apply details too. And you have to test to make sure whatever coating you use is compatible with the foam you use or the foam might dissolve. For something I made I used green floral foam with a high end body filler.
Most insulation foam is either EPS or XPS. You can cut and carve it best with a hot knife as it melts it instead of scrapping material of. If cut with a saw or anything that produces fine sand be sure to wear a mask as you don't want to inhale any of it. Same goes with the fumes. If you don't want to bondo the piece you could apply a layer of PVA glue to seal it before molding or painting as it will dissolve
Styrofoam is melted by polyester resin. It would have to be sealed/coated with a product like Styrospray instead, or possibly epoxy resin (not sure).

Better is to use polyurethane-based insulation foam or the hard green craft foam. Both are easily carved/sanded, and can be coated with either polyester or epoxy-based resins to create a hard shell for final surfacing.
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