Cthulhu Update
So, I have been experimenting with how to lay down the most optimal amount of foam. Because I am using a positive molding process (positive: material goes over a surface; negative: material goes into a mold), I have to contend with the material I lay down expanding in the wrong direction. The spray foam (e.g. Great Stuff) slowly and inexorably puffs in the direction of least resistence-- the air. When it sets it looks like a burn victim/bubble bath gone wrong. So, I started experimenting with corralling . The downside: it uses ALOT of duct tape. The upside: it does work. I have to take a one week break from this project. When I resume, I will try experimenting with tin foil (it's not just for hats anymore) plus some duct tape. If it goes very well, I may write a long piece of sculpting with Great Stuff foam and post it to " So Very Helpful ."