Many of the ones we cut apart don't seem to be glass ; there are certainly layers of plastic , but on some even the inner and outer surfaces seem to be some kind of plastic , or at least synthetic material .Laminated screens are glass on both sides with Perspex or similar sandwiched between.....never seen any screen with plastic outers,....they would last until the first time the wipers were used!!
However , some are indeed glass at least on the outside , that's why I was careful to say 'some' and 'many' as this does not apply to all of them .