What is heat-soaked glass?

Heat-soaked glass is simply glass that has been heat soak tested. Heat soaking is a kind of destructive glass strength test. It aims to limit spontaneous breakages in toughened and heat-strengthened glass by exposing the glass panels to extreme conditions. If the glass makes it through the test without breaking, it passes. If glass isn't heat soak tested, the risk of spontaneous breakage stands at around 0.01%. After testing, this risk drops to approximately 0.0001%.

When is heat-soaked glass required?

In rare instances, toughened and heat-strengthened glass can spontaneously shatter. This can happen for several reasons, including edge damage, vandalism and improper installation. It can also be caused by a rare phenomenon called nickel sulphide inclusion (NiS). This is where tiny particles of nickel sulphide are present in the glass after manufacture. NiS is natural. It's not considered a defect and it doesn't affect the appearance or clarity of the glass. However, it can cause spontaneous breakage when the glass is exposed to sudden temperature changes. Heat soak testing helps identify instances of NiS and dramatically reduces the risk of spontaneous breakage. For this reason, we recommend that all tempered and heat-strengthened glass is heat soak tested – especially if the glass will be installed in a hard-to-reach area.

What does heat soaking do to glass?

Heat soak testing does not affect the structure or appearance of glass. It serves to improve the quality of the glass we supply by rooting out panels that are vulnerable to spontaneous breakage.

What is the heat soak test procedure?

TG HST glass is tested in accordance with the industry standard: BS EN 14179-1. The process involves heating glass panels to around 290°C (554°F) and maintaining this temperature for two hours. The glass is then allowed to cool for a further two hours. Any breakages at this stage are replaced before the sequence starts again.

Can heat-strengthened glass be heat-soaked? What about laminated glass?

Any tempered glass can go through an HST test. This includes toughened glass and heat-strengthened glass. Laminated glass can also be tested if it's made using tempered glass.

Heat Soak Testing | Heat Soaked Toughened Glass

Give clients total reassurance with our EN 12150-certified tempered glass quality check.

Here at ToughGlaze, we recommend that all toughened and heat-strengthened glass is heat soak tested before installation.

Why? Because in rare instances tempered glass can shatter spontaneously after sudden temperature changes. This can be caused by several factors, including nickel sulphide inclusion (NiS).

It's important to note this isn't a defect. NiS is natural – and very rare. It's believed to occur in around one of every 400 tons of glass.

Heat soaking glass identifies these rare occurrences by simulating natural glazing conditions. Any affected glass sheets simply break during the testing process.

Give clients peace of mind and avoid costly replacements
Ideal for glass in hard-to-reach or public-facing areas
Tested in accordance with BS EN 14179-1:2016: the industry standard for HST glass
Quality comes as standard – all glass is sourced from just three trusted suppliers

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Heat-soaked toughened glass is recommended for any architectural glazing installation. However, it's most often specified for situations where the glass would be hard to reach and difficult to replace after installation.

These include:

Glass installed high above ground level
Glass in supporting walls
Large or specialised glazing units
Any glass that requires a crane or special equipment to install
Installations where breakages would pose a significant risk to the public

In these situations, choosing heat-soaked glass is like an insurance policy. It helps avoid unexpected costs and logistical headaches further down the line.

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Frequently asked questions

What is heat-soaked glass?

Heat-soaked glass is simply glass that has been heat soak tested.

Heat soaking is a kind of destructive glass strength test. It aims to limit spontaneous breakages in toughened and heat-strengthened glass by exposing the glass panels to extreme conditions. If the glass makes it through the test without breaking, it passes.

If glass isn't heat soak tested, the risk of spontaneous breakage stands at around 0.01%. After testing, this risk drops to approximately 0.0001%.
When is heat-soaked glass required?

In rare instances, toughened and heat-strengthened glass can spontaneously shatter. This can happen for several reasons, including edge damage, vandalism and improper installation.

It can also be caused by a rare phenomenon called nickel sulphide inclusion (NiS). This is where tiny particles of nickel sulphide are present in the glass after manufacture.

NiS is natural. It's not considered a defect and it doesn't affect the appearance or clarity of the glass. However, it can cause spontaneous breakage when the glass is exposed to sudden temperature changes.

Heat soak testing helps identify instances of NiS and dramatically reduces the risk of spontaneous breakage. For this reason, we recommend that all tempered and heat-strengthened glass is heat soak tested – especially if the glass will be installed in a hard-to-reach area.
What does heat soaking do to glass?

Heat soak testing does not affect the structure or appearance of glass. It serves to improve the quality of the glass we supply by rooting out panels that are vulnerable to spontaneous breakage.
What is the heat soak test procedure?

TG HST glass is tested in accordance with the industry standard: BS EN 14179-1.

The process involves heating glass panels to around 290°C (554°F) and maintaining this temperature for two hours. The glass is then allowed to cool for a further two hours.

Any breakages at this stage are replaced before the sequence starts again.
Can heat-strengthened glass be heat-soaked? What about laminated glass?

Any tempered glass can go through an HST test. This includes toughened glass and heat-strengthened glass. Laminated glass can also be tested if it's made using tempered glass.