Tempered & Heat-treated Glass

Tempered glass is used in safety glazing applications. Heat-strengthened glass is used when additional strength is needed.

ITI Glass manufactures tempered and heat-treated glass using one of the largest furnaces in the United States. The furnace incorporates advanced controls that enable ITI Glass to produce an extremely flat glass with optimal visual clarity.

Safety tempered glass

Tempered glass is used in safety glazing applications, including storefronts, interior glass walls and glass doors. The product is at least four times stronger than annealed glass of equal thickness and shatters upon breakage, meeting most safety glazing requirements. At ITI Glass, tempered glass is heated to 1400-degrees Fahrenheit in an electric furnace. After heating, the glass moves to the quench where it is rapidly chilled by a burst of air.

Rapid cooling leaves the glass surface in a state of compression and its core in a state of tension, which causes the glass to shatter in small pieces when broken.

Heat-strengthened glass

Heat-strengthened glass is used when additional strength is needed. Like the tempering process, heat-strengthening begins by heating glass in an electric furnace to 1400-degrees Fahrenheit. After which, the glass passes into the quench and is gradually cooled, resulting in a stronger product with a breakage pattern similar to annealed glass. Heat-strengthened glass is at least two times stronger than annealed glass of equal thickness. Due to its breakage pattern, the product is not used for safety glazing applications.


ITI Glass manufactures heat-treated glass according to ASTM C1048-04 and certifies all safety tempered glass in compliance with ANSI Z97.1-2004 and CPSC 16 CFR 1201 Category 2 standards.

Minimizing Roll-wave

During the heat-treating process, some amount of roll-wave distortion occurs as glass is heated, cooled and conveyed on ceramic rollers. However, many glass manufacturers recommend the following specification to minimize the appearance of roll-wave distortion in heat-treated float glass:

All heat-treated and fully-tempered glass shall be fabricated by horizontal process to show roll-wave distortion running parallel to the bottom edge of the installed glass (unless otherwise noted in these documents or drawings). Distortion shall fall within this accepted tolerance: A maximum of 0.005 inch from peak to valley in the center of glass, and a maximum of 0.0100 inch from peak to valley within 10-1/2 inches of the leading and/or trailing edges of the glass.

ITI Glass has established an in-house quality control program to manage roll-wave in its heat-treated glass. For projects requiring tighter roll-wave tolerances and production documentation, contact ITI Glass for more information.