Heat Strengthened glass

Heat-strengthened glass is a semi-tempered glass which retains the normal properties of ordinary float glass. It is similar to tempered glass except that the cooling is done slower than toughened glass but faster than annealed glass.
Heat-strengthened glass is about twice as strong as annealed glass.
Characteristics of Heat Strengthened Glass:
Heat-strengthened glass provides higher resistance to thermal stress when compared to annealed glass.
When producing Heat-strengthened laminated glass in comparison with Tempered Laminated glass, Heat-strengthened glass allows the interlayer to laminated glass to adhere more evenly because of a flatter finish surface.
As against toughened glass, Heat-strengthened glass - with its flatter surface - also results in the facade having less optical distortions.
This glass is difficult to break compared to ordinary annealed glass, but unlike toughened safety glass, breaks typically edge to edge and in fragments.
                    Breakage Pattern of Heat Strengthened Glass
Properties of HS Glass:


Heat-Strengthened Glass

Thermal Shock Resistance

Up to 130°C

Mechanical Strength

Two times stronger than annealed glass


Knife Edges

Tensile Strength

40-55 MPa

Bending Strength

40 N/mm2

Design Stress for Architectural Purpose

17 MPa

Benefits of heat-strengthened glass:
Heat-strengthened glass differs from tempered glass in surface compression; its mechanical strength is about 2 times that of annealed glass.
Compared to annealed glass, Heat-strengthened glass has higher thermal stability.
Heat-strengthened glass is 3 times more resistant to thermal stress in comparison to normal annealed glass.
While ordinary annealed glass can withstand up to 40°C, Heat-strengthened glass can withstand a temperature difference of 100°C (in range of 50°C to 150°C).
Heat strengthened glass is far less susceptible to spontaneous breakage.
Applications of HS Glass:
Heat-strengthened glass is popular among design professionals for vertical vision spandrel areas and for laminated sloped glazing. It is valued for its mechanical strength, which is twice of normal annealed glass, though half of fully tempered glass.
Heat strengthened glass has a comparatively flatter finish than fully tempered glass. Therefore, it has lesser optical distortions and can be used in places where high optical quality is required.
It can be used for general glazing where additional strength or resistance is required for mechanical/thermal loads caused by certain tinted or coated glass. The glass can also be used in high wind load areas, but cannot be used in any safety glazing applications, due to its breakage pattern similar to annealed glass.
Heat-strengthened glass is widely used in laminated glass for additional strength, such as in overhead and sloped glazing.