Wait...what? You made those awesome horses with plastic models and...foam?Tell me more!
The foam gives you a firm-ish base for epoxy clay, which does the real heavy lifting in the sculpting department. I used to stuff them with newspapers, but I learned that as the paper breaks down bad things can happen. The foam will last a lifetime, or so the foam lobby would have me believe.
Spray foam?How ingenius!
Impressed by your ingenuity! Are you taking orders? :-)