What are tempered glass windows?

What are tempered glass windows?

Curious about what tempered glass is? You're in the right place. This article explains what tempered glass is and answer some frequently asked questions regarding the material.

Simply put, tempered windows are windows made with glass that has been treated through a specific heating and cooling procedure that results in more durable and safer glass.

Typically windows that have the potential for human impact are legally required to contain tempered glass. You’ll find that windows in cars, bathrooms, and glass-enclosed showers are all made with tempered glass because of the safety risk glass in these places pose to humans. 

What is the difference between glass and tempered glass?

Tempered glass, also known as toughened glass, is a type of safety glass. The glass is treated by heat or chemicals, which increase its strength making it about four times stronger than single strength glass. Ordinary glass (annealed glass) is cooled more quickly than tempered glass and is much more fragile.

What is tempered glazing?

Glazing, or safety glazing, refers to glass that has been processed to be less susceptible to breakage and more importantly to reduce the potential for serious injury when it comes to human contact. Tempered glass and laminated glass are two of the most common types of safety glazing.

How is tempered glass made?

The glazing process for tempered glass begins with a preparation stage that includes cutting the glass to the desired size and examining the glass for imperfections. Next, the glass is put through a heat treatment in which the glass is heated to 600 degrees Celcius.

The heating treatment is followed by “quenching”, a high-pressure cooling procedure in which the glass is cooled in seconds. The quenching cools the outer surface of the glass more quickly than the center leaving the center in tension and the outer surface in compression, this is what gives tempered glass its strength.

The added endurance caused by the differential heating means the glass can be stretched or pulled to a certain limit without breaking. (Source: The Scientific American)

What are the benefits of tempered glass?

  • Safety: Tempered glass reduces the risk of injury due to its nature of breaking into small, circular pieces instead of sharp, jagged shards.
  • Easy clean up: Tempered glass isn’t indestructible. If the glass breaks it fractures into small fragments instead of large, jagged pieces.
  • Strength: Tempered glass is incredibly durable.

When is a window required to be made from tempered glass? 

According to the National Glass Association, there are 4 criteria that require safety glass:

  • The glazing (glass) is less than 18 inches above the floor
  • The top of the glass is less than 36 inches above the floor
  • The size of the glass exceeds 9 square feet
  • The glass is within 36 inches of where people walk

Any doors made of glass — sliding, French, or shower doors — are all always made of tempered glass.

**Consult your local building guides to confirm these parameters. 

Is tempered glass considered safety glass?

Yes, absolutely. The manufacturing process for tempered glass makes it 4-5 times stronger than ordinary (annealed) glass. This process also makes the glass less dangerous in cases of breakage.

Organizations began working to improve safety standards around the glass in the 1960s because hospitals were treating thousands of glass related accidents. Safety glazing standards resulted in fewer broken windows and doors and less severe laceration injuries and deaths. 

Is tempered glass bulletproof?

No. Tempered glass is not bulletproof, however, it is a component of bulletproof glass.

Can tempered glass break?

Yes. Tempered glass, like standard glass, can break. Tempered glass is designed to break into relatively harmless pieces when broken (some would describe it as small pebbles) as compared to the jagged shards of ordinary glass. This is still dangerous if it gets in your eyes or you fall onto it.

Does tempered glass shatter?

Not exactly, although tempered glass can break it does not shatter. Unlike ordinary glass (annealed glass), which shatters into sharp shards when broken, tempered glass is designed to break into smaller pieces.

Sometimes they don't disengage and instead interlock with neighboring pieces. If the pieces interlock and don't fall this is OK because you can see that the glass needs to be taken down immediately and replaced. If the glass interlocks and falls in clumps it can be dangerous because the edges are jagged and abrasive.

What causes tempered glass to break?

Tempered glass can be broken in many of the same ways ordinary glass is broken, especially if the tempered glass is defective. Spontaneous or delayed breakage is also characteristic of tempered glass. This means that if the glass is impacted at a pressure point the glass may not release (break) immediately, sometimes surprising people when it does break.


If you've been working on a replacement windows project or working with getting windows on a new construction house or building you've liking run into questions around tempered windows. We hope this article has been helpful to you and please reach out to us with any other questions. Hit the share button if you found this helpful!


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