The original safety glass on the market was wire glass and is still being used today in urban/contemporary styles and commercial applications. Next came laminated glass which is what your windshield glass is made of. Some older shower door glass may be this type of glass. Tempered glass is manufactured through a process of extreme heating and rapid cooling, making it harder than normal glass. It is not possible to alter/cut or drill tempered glass. It will shatter. Any extremely hot conditions such as fire will also cause tempered glass to shatter. One thing to remember is that tempered glass does not protect glass clarity or prevent hard-water stains.