Heat Strengtened vs. Tempered Glass

Are they referring to the same thing?

Heat-treating glass is a way to create glass with better durability and/or safety. The type of processing used depends on the intended application of the glass

There are two different types of heat treated glasses – heat-strengthened and tempered. The similarities between the two include:

• Production using the same processing equipment.
• Heating the glass to approximately 1,200 degrees F, then force-cooling it to create surface and edge compression.

The differences between the two glasses are as follows:

• With tempered glass, the cooling process is accelerated to create higher surface compression [the dimension of force or energy per unit area] and/or edge compression in the glass. It is the air-quench temperature, volume, and other variables that create a surface compression of at least 10,000 pounds per square inch (psi). This is the process that makes the glass four to five times stronger and safer than annealed or untreated glass. As a result, tempered glass is less likely to experience a thermal break.
• With heat-strengthened glass, the cooling process is slower, which means the compression strength is lower. In the end, heat-strengthened glass is approximately twice as strong as annealed, or untreated, glass.

Read more from the PPG Glass Education Center