Since the backside of the masks are modelnd , you would need to use a shader that allows transparency and then you would need to create / modify the texture of the mask to have a alpha channel ( depending on what shader you use) that defines what area should be transparent.
If you only need it to be transparent that a specific camera can look from the backside , it might be a option to have the mask on a separate layer, then exude that layer from the camera behind the mask.
That way you would avoid issues with the parts of the mask that are in fron but still visible from the back if you use transparency.