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Rigid foam in two part rigid mold - how deeply will I regret this

sheltatha_loresheltatha_lore ✭
in Lab work
I'd like to make some custom wig heads, ideally in expanding foam so they are light and I can pin into them.
That said, a head's worth of silicone is $$, and I don't need excessive amounts of detail - just an actual head-shaped head with facial features (no ears).  I also don't need more than a couple pulls.
How deeply would I regret attempting to cast rigid polyfoam into a two part plaster bandage mold?  (Assuming the mold is nice and smooth, it's been adequately released, etc.)  Looking at my head form, I think I can minimize undercuts with the right parting line and trimming off some of the neck, but there will probably be some minor undercuts even so.

I suppose an alternate solution would be a layer of flexible foam backed by rigid foam, but I'd like to avoid the extra materials and steps if they're not necessary.

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    Devin McdonaghDevin Mcdonagh ✭
    You can try lining the inside of the mold with plastic wrap to create a barrier, just make sure there are no gaps.  Once polyfoam gets a hold of plaster, it doesn't like to let go.
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    sheltatha_loresheltatha_lore ✭
    Oh, good idea! I was planning to completely slather it with vaseline, but plastic wrap can't hurt.
    Will small undercuts be a problem with foam, or will I be able to lever the material out? I don't think I can completely eliminate them without losing some shape.
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    Devin McdonaghDevin Mcdonagh ✭
    Vaseline is wise and it will help the plastic wrap hold to the surface.  You should be able to brute force the small undercuts.  you can block some of them by correcting them with the plastic wrap to a degree.  Kind of draping the plastic to eliminate the undercut or reduce it
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    sheltatha_loresheltatha_lore ✭
    Excellent. Thanks for the advice! I'll post some pictures once I make progress.
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    Chris EllerbyChris Ellerby Admin
    If you want something softer and self-skinning you could go with FlexFoam-iT 14.  https://www.smooth-on.com/news/flexfoam-14-skinning-urethane-foam/. But if you want a more rigid head, any other poly foams would work well.

    For releasing your mold, I second what was mentioned about doing a thorough job.  I would brush in a couple of thin layers of paste wax, then use a universal mold release that is compatible with the casting medium.

    /Chris
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