A windscreen or the car glass in the front of your auto window glass company or truck is not made up of a single sheet of manufactured glass. It's really 2 layers of glass that are divided by a complete layer of polyvinyl butyrate. This layer of PVB essentially glues as well as seals the two pieces of glass with each other. This serves several purposes, though the most important is to keep the stability of the windshield. In case of damage, the windshield is much less likely to ruin.