Heat-Strengthened Glass

In the architectural glass industry, it is a common belief that Tempered Glass (Fully Tempered) is always the best choice due to its high strength. However, interestingly, according to European Union standards, in many façade sections and sensitive building projects, using Heat Strengthened (HS) or semi-tempered glass is not only recommended but even mandatory.

What Is Heat Strengthened Glass?

Heat Strengthened Glass (HS) undergoes a process similar to Tempered Glass, with the main difference being a slower cooling rate. As a result, its thermal and mechanical strength becomes roughly twice that of regular annealed glass, while fully tempered glass is 4–5 times stronger.
But why, despite its lower strength, is European engineering moving toward HS glass?

Key Reasons Behind European Standards

1. Elimination of Spontaneous Breakage (Nickel Sulfide Inclusion)
The biggest drawback of tempered glass is the risk of spontaneous breakage caused by nickel sulfide inclusions. In high-rise projects, such incidents can be catastrophic. Because of its molecular structure and lower surface stress, HS glass nearly eliminates the risk of sudden spontaneous fracture.

2. Fracture Pattern and Retention in Frame
According to European standards, one major benefit of Heat Strengthened glass is its breakage pattern. Tempered glass, when broken, shatters into small pieces and falls out of the frame. In contrast, HS glass, like annealed glass, breaks into large fragments that remain in the frame.

Important Note:
When combined with laminated glass, if an HS layer breaks, the large fragments adhere to the PVB interlayer, maintaining the stiffness of the panel until replacement—preventing collapse.

3. Resistance to Thermal Shock
In modern façades where one section is in direct sunlight while another is shaded, thermal stress can be intense. Heat Strengthened glass resists thermal stress effectively and, unlike full tempered glass, causes less optical distortion, leading to smoother and more visually flat façades.

Applications Required by Standard

• Glass façades (Curtain Walls): Especially in upper floors where the risk of falling glass particles must be prevented.

• Spandrel Glass: Areas behind opaque façade panels where heat absorption is high.

• Laminated Glass Stairs and Railings: To maintain structural integrity after possible fracture.

Conclusion for Builders and Architects

Using HS glass reflects a deep understanding of glass engineering principles.
At Arshia Jam Factory, with our GLASTON RC350 VORTEX PRO-CONVECTION furnace—one of the most advanced and fully European-standard machines—and our dedicated production recipe for genuine Heat Strengthened (HS) glass, we deliver the highest quality and reliability for your critical projects, ensuring maximum safety and aesthetic excellence.