Early windshields were made of ordinary window glass, but that could lead to serious injuries in the event of a crash. A series of lawsuits led up to the development of stronger windshields. The most notable example of this is the Pane vs. Ford case of 1917 that decided against Pane in that he was only injured through reckless driving. They were replaced with windshields made of toughened glass and were fitted in the frame using a rubber or neoprene seal. The hardened glass shattered into many mostly harmless fragments when the windshield broke. These windshields, however, could shatter from a simple stone chip. In 1919, Henry Ford solved the problem of flying debris by using the new French technology of glass laminating. Windshields made using this process were two layers of glass with a cellulose inner layer. This inner layer held the glass together when it fractured. Between 1919 and 1929, Ford ordered the use of laminated glass on all of his vehicles.
Modern, glued-in windshields contribute to the vehicle’s rigidity, but the main force for innovation has historically been the need to prevent injury from sharp glass fragments. Almost all nations now require windshields to stay in one piece even if broken, except if pierced by a strong force. Properly installed automobile windshields are also essential to safety; along with the roof of the car, they provide protection to the vehicle’s occupants in the case of a roll-over accident.
Today’s windshields are a safety device just like seat belts and airbags. The installation of the auto glass is done with an automotive grade urethane designed specifically for automobiles. The adhesive creates a molecular bond between the glass and the vehicle. If the adhesive bond fails at any point on the glass it can reduce the effectiveness of the air bag and substantially compromise the structural integrity of the roof.