Tempered glass is four times stronger than "normal" glass or annealed glass. Unlike annealed glass, broken into jagged fragments, broken glass into small, relatively harmless fragments. Therefore, tempered glass is used in the environment of human security issues. Applications include side and rear windows for vehicles, entrance doors, shower and bath rails, squash courts, patio furniture, microwaves and skylights.

To prepare the glass for tempering, you must first cut it to the desired size. (A reduction in strength or product failure occurs if any manufacturing operations, such as etching or milling, are performed after the heat treatment.) The glass is then checked for flaws that can lead to cracking during any step during tempering. Matte materials such as sandpaper leave a sharp edge from the glass and are then cleaned.

The glass inspector checks a piece of toughened glass for bubbles, stones, scratches or any other imperfections that may weaken it.

Next, the glass begins a heat treatment process in which the glass passes through the tempering furnace in a batch or continuous feed. The oven heats the glass to over 600 degrees Celsius. (Industry standard is 620 degrees Celsius). The glass then undergoes a high-pressure cooling process called "quenching." During this duration of a few seconds, the high pressure air exits the glass surface from a different array of nozzles. Quenching is much faster than cooling the outer glass surface of a glass center. When the center of the glass cools, it tries to pull it back from the outer surface. As a result, the center maintains its tension and the outer surface enters a compressed state so that the strength of the tempered glass.

Glass is about five times more likely to break in tension than in compression. The annealed glass will crack at 6000 pounds per square inch (psi). According to federal specifications, tempered glass must have a surface pressure of 10,000 psi or higher; it typically cracks at about 24,000 psi.

Another method of making toughened glass is chemical toughening, where various chemicals exchange ions on the glass surface to produce compression. However, this method is not widely used due to its much higher cost than using tempering furnaces and quenching methods.