By default, if you look at outside from the inside of a model, the reversed faces/normals appear to be invisible in Unity. Is it possible to make the reversed faces render as black (Without any reflections)?
You’d have to write your own shader, but it is possible to make a distinction between front and back faces. Shader model 3.0 is required and then you can use the VFACE register. (And turn backface culling off of course.)
If you’re unable to write this shader, copy, flip, export and put a black material on it.