How much do you know about tempered glass?
Release date:
2025-09-01
Window and door glass is an essential component of any window or door—after all, it’s what makes these elements functional and secure. In the past, windows and doors typically featured single-layer glass, but today, advancements have led to the development of innovative options like insulated glass, laminated glass, and even bulletproof glass. Among these, insulated glass remains the most commonly used in architectural applications. And when it comes to insulated glass, tempered versions are widely regarded as the best choice.
How can you tell if insulated glass is tempered?
The simplest and most straightforward method is to simply look—check if the bottom corner of the glass has the 3C certification mark for tempered glass. Glass with the 3C marking is almost always tempered (though in most cases, the mark can’t be easily scraped off).
Tempered glass is produced by first cutting standard float glass into the desired size, followed by edge grinding, cleaning, and applying the mandatory national CCC certification mark—typically done using regular ink. Afterward, the glass is heated in a tempering furnace to become fully tempered. Once this process is complete, the glass cannot be further cut or reshaped.
Because of the specific equipment and manufacturing processes involved, tempered glass may occasionally exhibit minor quality defects. A common way to identify such defects is to inspect the glass surface for any visible distortions.
Another reliable method is to gently tap the glass; if it’s truly tempered, it should remain intact even under light impact. If you’re still unsure after checking for the 3C mark, give it a good whack with a hammer—or even stomp on it with your foot—and you’ll find it won’t shatter at all.
Here's a photo featuring the tempered glass logo.
Below are two more images: one shows the fragmented state of tempered glass after it has broken, and the other captures the moment just after the tempered glass was shattered but before it hits the ground.
Tempered glass is produced by processing ordinary flat glass or float glass through specialized techniques. For ordinary flat glass, only specially selected or first-grade products are suitable; for float glass, only superior- or first-quality glass is acceptable. There are two primary methods used to manufacture tempered glass:
1. One method involves subjecting ordinary flat glass or float glass to controlled thermal treatment—either through quenching or air-cooled quenching—to enhance its strength and durability.
2. The other method uses ion exchange, altering the chemical composition of the glass surface to create a compressive stress layer, thereby improving its mechanical properties.
Tempered glass boasts exceptional characteristics, including significantly higher impact resistance (4 to 5 times greater than regular flat glass), superior bending strength (up to 5 times stronger), excellent thermal stability, and a smooth, transparent, and non-cuttable finish. Moreover, when subjected to extreme impacts that cause it to shatter, tempered glass breaks into small, evenly dispersed particles without sharp edges—making it inherently safer and earning it the title of "safety glass."
Whether it's PVC windows and doors with tempered glass, or aluminum-framed windows and doors with tempered glass—both are commonly seen in everyday life. They’re particularly often used at the bottom of high-rise residential building windows and doors, as well as in floor-to-ceiling windows.
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