expanding foam

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Well-Known Member
Jan 20, 2009
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I am trying to make a vacuum formed copy from a vacuum formed master. The master is hollow (it's the Estes space shuttle) and I need to fill the inside so it doesn't collapse. My first thought was to use some sort of expanding foam, but I'm worried about it attacking the thin plastic of the shuttle. Can anyone offer any advice about this stuff? - brands, types, etc. About the only experience I have is using it to seal around the outside of my house!
Drew Tomko
I don't know about the chemical compatibility, maybe you could spray the interior with a couple coats of ????? to address that.

The foam is going to add a bit of weight. You could estimate how much by constructing a small cardboard box of similar dimensions and foaming it. (You will need to weigh it before and after)

You definitely need to be careful that the expanding foam does not push your thin-skin model out of shape. You could drill lots of vent holes, but that will also make lots of mess at the later finishing stages. You could enclose it in something but that could be as much trouble as foaming the interior.

Are you sure you can't do something like a sheet-n-stick-balsa framework on the interior (model airplane style)?
Weight isn't a concern because it's just a master. Pushing it out of shape is, however, a big concern. It's open on two sides, so that the excess can easily get out. I did think of making some sort of framework, but that would probably pucker under the vacuum forming. I may just stuff modeling clay in the inside and stick it in the freezer before forming.
How about using a two part epoxy to coat the inside of the shuttle? Once the epoxy sets it would really strengthen the whole thing, and you could add another layer if needed, or use another type of filler without much fear of damaging the shape of the shuttle.
Thanks for the suggestions. I hadn't considered the epoxy option. I think I'll try that first since I have it on hand.