I know foam can do amazing things, but most of the 405th stuff I've seen in this callable was usually fiberglass pepakura. Thou I could be wrong. The stomach has to be foam else he wouldn't be able to move.
thanks guys to let you know its 100% eva foam floor mats and just the run of the mill Walmart hot glue. the pattern is a little custom but I used a pep file that will cherry from the 405th designed he is letting people have a copy if you donate to there fan film dawn under heaven.