In the early Modern 1900's, a windshield was cut by hand using regular glass and was fitted in the frame using a rubber or neoprene seal. These windshields protected vehicle occupants from wind and rain but nothing more.
Then in 1919 along came Henry Ford who introduced the laminated windshield, which consisted of two sheets of glass with cellulose centre layer between them for safety. Today the laminated windshield is curved not flat and a polyvinyl butyral (PVB), which is a high-strength vinyl, is used instead of the inferior cellulose.
Over the years, the installation process of a windshield has also evolved for safety; as a Windshields primary role is not just to protect the vehicle's occupants from wind, rain, and flying debris, a properly installed windshield is essential to safety.
Until the late 1970's and early 1980's, glass installers used a petroleum based adhesive called butyl tape to install a windshield. Butyl tape required no curing or hardening and had only a fraction of the strength and durability of the urethane used today.
Today a windshield responsible for a major part of the structural integrity of the vehicle, the role once held by the steel frame which means that along with the roof of the car, the windshield provides protection in the case of a roll-over accident. With that information in mind its important to point out that a windshield in today's late model automobile is installed with urethane. Urethane is a specially formulated glass bonding system designed to meet OEM durability specifications and Federal Motor Vehicle Safety Standards (FMVSS) for barrier, rollover and roof crush regulations.
A correctly fitted, expertly installed windshield means that your vehicle is restored to its original strength.