Heat Treated Glass

Frequently Asked Questions About Heat-Treated Glass Products

What is Heat-Treated Glass?

Heat-treated glass is annealed glass that has undergone a tempering thermal process to increase its durability, enhance resistance to mechanical stresses, and make it safer in case of breakage by achieving specific break patterns. After cutting the annealed glass panel(s) down to the required dimensions, each panel is transferred to a furnace where it is heated to a high temperature and then rapidly or slowly cooled by blowing air onto both sides simultaneously.

Is Heat-Treated Glass the Same as Tempered Glass?

While the terms “heat-treated” and “tempered” are sometimes used interchangeably, they do not mean the same thing. There are two types of heat-treated glass: heat-strengthened and fully tempered. While both types of glass undergo a heating process, they utilize a different cooling process to produce different results.

Heat-strengthened glass uses a slower cooling process to produce a finished product with a high surface quality that is twice as strong as annealed glass. Heat-strengthened glass retains the break pattern of annealed glass, however, making it a poor choice for applications requiring a high level of safety.

Fully tempered glass utilizes a faster cooling process to increase surface compression and edge compression. This creates a product that is roughly four times stronger than annealed glass while providing a unique break pattern consisting of smaller particles. This makes fully tempered glass a great choice for applications requiring a higher degree of safety, earning it the title of “Safety Glass”.

Where is Heat-Treated Glass Used?

Heat-treated glass is used for applications that require enhanced durability and safety. While heat-strengthened glass cannot be used in safety glazing applications, tempered glass can. These applications include sliding glass doors, windows, display cases, bath/shower enclosures, all-glass doors, and partitions. At PFG Glass, all of our heat-treated glass products are SGCC (Safety Glazing Certification Council) certified for use in safety glazing applications.

How Can You Tell if Glass Has Been Heat-Treated?

Heat-treated glass will likely not be as flat as annealed glass due to the heating and cooling processes. While some providers can minimize warping and optical distortion by using high-quality equipment, this can still occur for some panels. Heat-treated glass may also display visible strain patterns, also known as quench marks. These typically appear as geometric patterns of iridescence or dark shadows, but only under certain lighting conditions. Strain patterns are an inherent characteristic of heat-treated glass and are therefore not considered to be a defect.

What are the Benefits of Heat-Treated Glass?

Heat-treated glass is far stronger and more durable than annealed glass. Heat-strengthened glass is twice as strong as annealed glass, while fully tempered glass is four times as strong. Fully tempered glass also features a unique break pattern when compared to annealed or heat-strengthened glass. While the latter options break into large and sharp pieces, the former breaks into small dice-sized pieces that are not as sharp. This significantly reduces the risk of injury should a break occur, making it a required choice for applications requiring safety glass.