Vacuforming a buck made from reinforced rigid foam insulation?

[Ein]

So I have to make some quick armor molds for a vacuform table test and I'm wondering what the easiest material to work with is. I'm trying to make torso-sized armor. I'm debating getting a cube of rigid home insulation foam, like this stuff:

... and then carving it with a hot knife. Obviously the foam will get totally wrecked if I try vacuforming it straight, but I'm wondering if there's something I can skin it with like Bondo or similar that would hold up to the vacuum forming process and let me get some clean pulls of PETG off. I see people making bucks out of MDF instead, but I honestly don't know how I could carve the shapes I need out of that without a metric ton of labor.

 

[GaryArm]

Bondo skin would work for your first pressing. But your buck may get damaged during removal, I would then re fill the plastic shape with plaster to make a new buck. Don't use resin to strengthen the surface of a buck a the hot plastic will welt the resin and glue the plastic to the buck

 

[wondersquid]

Doing a mixture of Bondo and Fiberglass resin then pouring it over the foam will help seal it. Polyurethane resin can do the same, but just watch the heat, make sure it doesn't warp your piece. You will need to sand this coating to get it perfectly smooth, but short of using 1630, this is probably your fastest and cheapest route.