molds for expanded foam
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Sorry for replying to such an old thread. Most of the molds for polyurethane foams that I've made (especially for larger parts) have been epoxy/fiberglass molds. I'm not sure about the tooling board. One of the things you need in this type of mold is to create some degree of backpressure on the expanding foam so that the foam will skin properly at the surface. Very small vent holes in areas where air might be trapped are a good idea, 1/16" should generally be sufficient, not affecting the backpressure much or allowing lot's of foam out of the mold. It depends on the size of the mold, but if it's not too large just the pour spout should be enough to moderate the backpressure, it really varies a lot depending on the shape and thickness of the piece and the volume of foam you are pouring.
It can create an awful lot of pressure if you pour too much foam in the mold, so it's pretty important to know what the volume of the final piece is. From there, it's not hard to calculate how much foam you need. For a rough example, your pieces volume is 10 gallons. The foam expands to 8 times it's liquid volume. So 1.25 gallons of foam (mixed) should exactly fill the mold. But you want a little backpressure, and sometimes depending on temperature and humidity variations the foam may not expand exactly to spec, and I'd usually add perhaps 5-10% more foam to make sure it fills and skins properly.
Most of my experience with the stuff has been for casting pretty large skin sections for animatronics. But I've also done plenty of smaller pieces in ultracal or Forton MG molds. It's not a super critical thing. Almost anything that is reasonably strong and rigid should work.
