Glass

It doesn't happen painlessly. (Lol) It is a pain to get off and what makes it worse is the defroster. Get a spray bottle and put a small amount of dish soap in it and then fill it with water. You need to start pealing the tint off and then spray it with the soapy water to soften it. Then peal a little more away. The soap usually helps soften it. Thus, it comes off easier (but not too easy).