Heat-Strengthened Glass

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Last Updated: July 30, 2024

Heat-strengthened glass is a type of thermally treated glass that has been specially processed to enhance its strength and resistance to windload and thermal stress. It is approximately two times stronger than annealed glass of the same thickness in resisting windload.

In the event of breakage, heat-strengthened glass typically fractures into large sections, akin to annealed glass, and usually remains in place within the opening.

Heat-strengthened glass is ideal for scenarios where regular annealed glass does not meet thermal or windload requirements. It can be used with all Cardinal LoĒ™ coatings, tinting, reflective vision glass, and is a recommended option for spandrel applications.

Heat-strengthened glass meets the ASTM C1048 specification, which requires that 6mm glass have a surface compression of 3,500 to 7,500 psi (24-52 MPa). This makes it a reliable option for areas requiring increased resistance to thermal stress and wind pressure, but where tempered glass is not required.

Heat-Strengthened vs. Tempered Glass

Heat-strengthened glass and tempered glass are both thermally treated to enhance their strength, but they differ in several aspects:

Strength: Heat-strengthened glass is about twice as strong as annealed glass in resisting windload, whereas tempered glass is approximately four times stronger.
Breakage Pattern: Heat-strengthened glass breaks into large sections similar to annealed glass, usually remaining in the opening. Tempered glass, however, shatters into small, less hazardous fragments.
Thermal Treatment: Heat-strengthened glass, while stronger than annealed glass, does not meet safety glazing standards and is not considered safety glass, as defined by ANSI Z97.1 or CPSC 16 CFR 1201. In contrast, tempered glass is heated to higher temperatures and more rapid cooling than heat-strengthened glass, which enhances its surface compression and overall strength. This process qualifies tempered glass as safety glazing, suitable for use in doors and similar applications.
ASTM C1048 Standard: Heat-strengthened glass must have a surface compression between 3,500 psi and 7,500 psi (24-52 MPa). In contrast, fully tempered glass requires a surface compression over 10,000 psi (69 MPa) or a minimum edge compression of 9,700 psi (67 MPa).

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