Looking at the Scorpius makeup from Farscape (the first use of Hotflesh), it is definitely NOT foamed anything. Foaming introduces all those tiny bubbles which in turn make the material more-or-less opaque.
I wonder what the HECK he is using? I still bet on a variation of hot pour pvc, but at this point I haven't got a good clue at all.
I still think that foamed hot-pour will make an interesting material, though. I wonder, though, how the oils will react with skin? I don't think I want to use it on the face, but as stand-alone body parts. This way I get some weight to them, they wobble nicely, and they are cheap.
Foam latex doesn't have the right wobbly feel for these things and silicon is too darned expensive.
Hmmm... foamed silicon?
Wheee!