In regards to the appleseed helmet, it was originally modeled by chwbcc. This is a rough model for people to play around with, but he has already stated that he will release a final, cleaned up model. In regards to the outer skin, they are the same layer. If you play around with all of the different components of the model, there are the individual pieces, and then one fully assembled all in the same file. There are no inner and outer meshes to it.