- At the start, tempered glass is formed and fabricated just like untempered glass. Unlike regular glass, however, once fabrication – that is, its manufacture into the end product – is complete, the glass is placed into a furnace and heated to its melting point. When the glass becomes soft, it's moved into a quenching chamber and rapidly cooled. This process gives tempered glass four to five times more strength than untempered glass.
- Tempered glass is considered safety glass, and is preferred for a number of applications, including windows. It's used in vehicle windows to minimize injury in accidents by reducing deadly shards and by keeping passengers inside the vehicle. It's used for windows in buildings, because it's more thermally stable and less likely to break from temperature changes. Tempered glass is also a safer choice for use in furniture because it doesn't shard when broken.
- Due to the tempering process, panes of glass may show reflection distortion. When the glass is heated and cooled so quickly, a small amount of warping occurs throughout the pane. You may also see roller marks within the glass. In applications where complete clarity is important, regular annealed glass should be chosen.
- Not all heat-treated glass is tempered. While tempering involves high heat and rapid cooling, adjustments can be made to the temperature of the heating chamber and the quenching air temperature – quenching is the cooling portion of the furnace – for a resulting heat-strengthened glass. While stronger than untempered glass, this variety is not as strong as tempered glass, as it is has been processed at lower temperatures and cooled, or quenched, more slowly.