Bullet proof glass
Everyone calls it bullet proof glass but in reality nothing is bullet proof. The term for it is bullet resistant because if something is shot enough, one will find its way through eventually. Bullet resistance glass is a combination between very thin sheets of glass and even thinner sheets of tough plastic made of polycarbonate. This is able to work because as the bullet hits the glass it breaks the thin sheets of glass and the energy from the bullet is absorbed by the plastic layers. To make this effective you increase the number of layers to absorb more energy. The ratio between glass to plastic is normal 3:1 were the layers of plastic are 1-3 mm thick and the glass is 3-10 mm thick. This is crazy to think that by layering glass and plastic it is able to stop a .308 caliber marine sniper bullet, one that will knock you off your feet entirely. In this video you can see that this glass is only successful for two shots from a .308 rifle at close range. So if you are in a car with a sniper shooting at you and have this glass between you and the bullet, I would suggest driving pretty fast.