Heat Strengthened and
Fully Tempered Glass

What is the difference between heat-strengthened and fully tempered glass?
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What is the difference between Toughened (TGH or HT) and Heat-Strengthened (HS) glass? How do I determine which is needed for my project?

Toughened (also known as tempered) glass is approximately four times stronger than regular annealed glass of the same thickness and configuration. When broken, it usually breaks into many relatively small fragments, which are less likely to cause serious injury in most applications. Toughened glass is often referred to as “safety glass” because it meets the requirements of various code organizations for safety glazing. This type of glass is usually intended for sliding doors, building entrances, bath and shower enclosures, interior partitions and other uses requiring superior strength and safety properties. Toughened glass cannot be cut or drilled after toughening, and any alterations, such as edge grinding, sand blasting or acid etching, can cause premature failure. In Europe, toughened glass is produced according to the EN12150 standard.

Heat-strengthened (HS) glass has been subjected to a specifically controlled heating and cooling cycle, and is generally twice as strong as annealed glass of the same thickness and configuration. It has a greater resistance to thermal loads than annealed glass and when broken, the fragments are typically larger than those of toughened glass and initially may remain in the glazing opening. Heat-strengthened glass is not a safety glass product as defined by building codes, unless it is in its laminated form. It is intended for general glazing, and is usually the choice for commercial applications where additional strength is desired to withstand wind load and thermal stress, but the strength of toughened glass is either not necessary, not required by building safety codes or is of concern because of NiS related spontaneous failure. HS glass can’t be cut or drilled after heat-strengthening and any alterations, such as edge grinding, sand blasting or acid etching, can cause premature failure. In Europe, heat-strengthened glass is produced according to the EN1863 standard.

It is important to note that the heat-treating process creates optical distortion that can be reduced but not eliminated. Guardian recommends that the glass manufacturer or fabricator be consulted, and mock-ups be viewed and approved whenever possible.