Identification of Tempered Glass

by Scott Cornell; Updated September 26, 2017

Tempered glass, or toughened glass, is engineered to be four to six times stronger than average glass and to withstand higher temperatures. Tempered glass is commonly identified by its properties and the applications it is used in.

Mechanical Properties

Unlike traditional glass, which shatters into sharp, dangerous shards, tempered glass shatters into small, square shaped pieces, a safer alternative in the event of a crash. It takes a strong impact to the middle of a pane of tempered glass to break it. It may only break when the edges of the pane become damaged.

Chemical Properties

Tempered glass can withstand temperatures up to 470 degrees Fahrenheit. If it is exposed to higher temperatures, it will gradually weaken, making it more prone to damage. Prolonged exposure to 600 degrees Fahrenheit or greater eventually will cause the pane to shatter into small pieces.


Tempered glass is used in applications where heat, mechanical strength and safety are important factors. For example, the windshield and windows of the cars you see driving on the road every day likely are made from tempered glass. This makes it much less dangerous for a motorist in the event that it damages or cracks. Another use for tempered glass is fireplace doors, where it is strong enough to withstand the high temperatures of burning wood.

Manufacturing Tempered Glass

Tempered glass begins as regular glass. It is then "annealed," or uniformly heated and then cooled at a consistent rate. Once cooled, the glass is brought down to room temperature as a more durable glass. It undergoes a "tempering process," where it is heated in a furnace to more than 600 degrees Celsius, then immediately cooled with air jets. This makes the surface cool and stiff, while the core gradually cools and hardens. Note that after the glass is tempered, it cannot be cut or shaped. It must be shaped prior to tempering.

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