Heat-Strengthened Glass

Insulite fabricates heat-strengthened glass on three state-of-the-art electric horizontal oscillating furnaces. The furnaces will heat-strengthen 1/8” (3mm) to 3/8” (10mm) thick flat float glass products. These furnaces are equipped with two hearths for increased output and aspirators for heat-strengthening the new generation of post heat- treatable vacuum deposited reflective and low-e glass products available today.

The furnaces heat the glass to a uniform temperature of approximately 1200 degrees Fahrenheit. Ceramic rolls convey the glass through the furnace at speeds regulated to ensure temperature uniformity and minimal optical distortions. The heat-strengthening process parallels the process of tempering, except that the cooling cycle is less rapid, therefore, creating surface compression levels less than fully tempered glass.

Heat-strengthened glass has approximately twice the mechanical and thermal strength of annealed glass of equal thickness. Heat-strengthened glass normally has a break pattern of large pieces similar to a break pattern of annealed glass, with other breakage patterns possible, as illustrated on this sheet. Heat-strengthened glass is used in areas requiring added strength to the glass but a larger break pattern than that of tempered glass so that the broken glass remains in the opening until it can be secured for a replacement. The most common use of heat-strengthened glass is in spandrel glass locations. Heat-strengthened glass cannot be cut or drilled after heat strengthening.

Heat-strengthened glass does not meet safety glazing requirements of ANSI Z97.1 and CPSC 16 CFR 1201.

Optical quality:

Bow, warp and process roll distortion may be evident. This is an inherent characteristic of the manufacturing process and is within the limits set by ASTM Standard C1048.


ASTM C 1048 Standard Specification for Heat-Treated Flat Glass.

For additional information and size limitations of heat-strengthened glass contact Insulite.