What is tempered glass?

Tempered glass is safety glass that has been heated in a tempering furnace and then cooled rapidly. This makes it about four to five times stronger than ordinary float glass and much better at handling thermal shock. If it does break, it falls apart into small granules instead of large, sharp shards.

Tempered glass is often used for a kitchen splashback, interior and exterior doors, shower and bath screens, and table tops.

What happens during tempering?

First the glass is cut to size and given the required edge finish and other processing. Then it goes into a tempering furnace of about 650 °C, where the glass softens and expands. Once it is soft enough, it is cooled as quickly as possible with cold air. The outside shrinks and hardens immediately, while the inside cools and shrinks later. This creates tension in the glass, and that tension makes it so much stronger. Because the glass is processed first and tempered afterwards, you cannot cut, drill or grind tempered glass once it has been tempered.

Types of tempered glass

As with ordinary glass, there are many options. Tempered glass is always at least 4 mm thick; depending on the application and the size, you choose thicker glass. Besides clear glass, you can also have coloured glass and some types of patterned glass tempered.

Advantages of tempered glass

• about four to five times stronger than ordinary glass, with a high bending strength
• can handle a temperature difference of approx. 200 °C (untempered glass much less)
• resistant to extremely low temperatures
• good resistance to blunt objects
• breaks into small granules, so the risk of serious injury is much lower
• suitable for table tops, furniture, shelves and kitchen splashbacks; for shower screens and shower doors we recommend at least 8 mm

Disadvantages of tempered glass

• less resistant to sharp or pointed objects
• cannot be processed after tempering
• does not prevent falling through: where someone could fall down, laminated or tempered laminated glass is needed
• strong, but not unbreakable: in rare cases it can break spontaneously because of a tiny nickel sulphide particle in the glass

The difference with laminated glass is explained in Is laminated glass always tempered glass?. Where safety glass is needed is covered in Do I need to use safety glass?.