What Is Laminated Safety Glass?

Laminated safety glass consists of two or more sheets of glass bonded together under heat and pressure with a transparent flexible plastic called polyvinyl butyral, according to Glasslinks.com. When the glass is struck, it breaks but the shards are held together by the plastic inner layer. Laminated safety glass began appearing in automobile windshields in 1927, but it had been invented more than two decades earlier. It was also used in auto side windows through 1959, when it was displaced by cheaper tempered safety glass. Tempered glass is more resistant to breakage, but when it breaks, it shatters into many little blunt pieces.

Story of Invention

French chemist Edouard Benedictus was working in his lab in 1903 when he accidentally knocked a flask to the floor, according to invention history website IdeaFinder.com. Instead of shards scattering all over, the broken pieces had stayed together. The flask hadn't been cleaned since holding cellulose nitrate, a transparent liquid plastic. The clear plastic residue had kept the glass pieces together.

Practical Idea

Benedictus had read about auto accidents where occupants had been severely injured by shattered glass windshields, and he thought shatterproof glass could be a boon to auto safety. He experimented with different laminating plastics before finding one that worked well, and sought to sell his invention.

Lack of Interest

But before World War I, automakers weren't interested because of the cost and the prevailing attitude that safety was the responsibility of the driver, not the manufacturer, according to IdeaFinder. The first widespread use of laminated safety glass was in the lenses of gas masks, where it performed superbly in World War I. Automakers' attitudes toward safety glass changed as fully enclosed cars came into fashion, and the first autos equipped with laminated safety glass windshields appeared in 1927. By 1937, most automakers were using laminated safety glass on all windows.

Other Uses

Auto windows aren't the only use for laminated safety glass. It also has many architectural uses, says Oldcastle Building Envelopes. Laminated glass products are used for skylights and sloped glazing in museums, hotels, schools and office buildings as well as for glazed areas of interior partitions.

High-Security Applications

Laminated safety glass is ideal for high-security applications, said Oldcastle. It's the glazing of choice for bomb-resistant buildings and for bulletproof armored windows in places such as prisons, government buildings, banks or jewelry stores, because it stays in the frame despite heavy impact. Special heat-strengthened laminated glass is sold for windows in hurricane- or earthquake-prone areas.