Say you made your model out of cardstock, that would make paper your surface....
Then you put all these layers of fiberglass under the armor to re-enforce it. What do you use to protect the outside from getting all screwed up (say you want to do some heavy duty playin around in it... ;-) )
what i am doin is that i take references from pics, use hot glue and glue them together, i have filled the inside with expanding foam, and right now i am in the process of sanding the great stuff, and i dont know how to make the outside hard.
The last time I used spray foam I underestimated its expanding properties. And lets just say my mandolorian helmet split open like a squashed grape. LOL