They're made of semi hard rubber (not eraser soft, sturdy but flexible). I left all of the headers attached to the board and just cut the bags to get them out. They were a gift from a friend in Japan. I'd never seen them before receiving them, but I really like them.
this is the first time i've seen this kind of toy with articulation. i wouldn't think this kind of material would hold a hinge very well, that flip mask is a great idea.