Tempered glass options, Toughened vs. Heat Strengthened Glass: Understanding the Differences
When it comes to boosting the strength performance, removing thermal fracture and durability in glass, two common treatments stand out: toughened glass and heat strengthened glass. At Viridian, we often get asked which is the better choice. The answer depends on the application of the glazing, its performance requirements, safety standards, and design priorities. Let’s break down the differences.
What Happens in a Glass Furnace?
When we temper glass to create either heat strengthened or fully toughened glass, they are both produced using the same furnace. Both processes include a heating phase where we heat the panels back to almost melting point, before transferring them out of the furnace and into a quench, which is a chamber where high capacity fans blow air directly onto the panels. This quenching process is more intense when toughening and carried out relatively quickly to lock in the resultant surface tensions. For a heat strengthening profile, less intensive air and longer quench times are used.
Heat Strengthened Characteristics
This surface strength is increased to about twice that of ordinary annealed glass.
Key Characteristics
- Strength: Roughly twice as strong as standard float glass.
- Breakage pattern: Breaks into large angular fracture shards which generally run to the panel edge (not as safe as toughened).
- Distortion: Less roller wave and optical distortion compared to toughened glass, making it suitable for large façades or applications where visual clarity is critical.
- Thermal resistance: Can withstand significant temperature changes within the panel of around 180 degrees
- Cannot be further cut or processed
Common Applications and Advantages
- Elimination of thermal risk in facades
- Significantly more economic and faster lead-times when used as an alternative to remove heat soaking processes from toughened applications
- Heat Strengthened laminates are commonly used in overhead glazing and some balustrading applications, where the larger fracture pieces provide greater rigidity by adhering to the interlayer in the case of dual panel failure.
- Spandrel panels, and facades where if broken, the shards remain better retained by the framing elements
Toughened Glass Characteristics
Toughened (or tempered) glass undergoes a similar heating process but is cooled much more rapidly. This creates a surface compression up to four to five times greater than annealed glass, making it the strongest of the two options.
Key Characteristics
- Strength: Four to five times stronger than annealed glass.
- Breakage pattern: Breaks into small, blunt fragments – reducing risk of serious injury.
- A grade safety glazing material: When processed to the requirements of AS2208 – Safety glazing materials, meets the definition within the glazing standard AS 1288 for Grade A safety glass.
- Thermal resistance: Handles temperature differences of up to 250°C.
- Cannot be further cut or processed
Common Applications
- Used where A Grade safety materials are called up on the glazing standard AS1288
- Where is increased strength is needed to withstand high load conditions, such as Wind Loads, and as components in structural laminates for balustrades, overhead glazing etc.
- Frameless doors, shower screens, and other high-impact areas or where structural and mechanical fixings are used to retain panels in place.
- Limited to panel fall heights of less than <5m unless additional heat soak process is included.
Side-by-Side Comparison
| Feature | Heat Strengthened Glass | Toughened Glass |
|---|---|---|
| Relative Strength | ~2x stronger than annealed | ~4–5x stronger than annealed |
| Breakage Behaviour | Large sharp shards | Small blunt fragments |
| Safety Rating | Not safety glass | Grade A safety glass |
| Optical Distortion | Lower (better visual flatness) | Higher (roller wave may be more visible) |
| Thermal Resistance | High | High |
| Typical Applications | Curtainwalls, Spandrels, Façades, laminated combinations for overhead glazing | Balustrades, doors, safety-critical areas |
Choosing the Right Glass for Your Project
- For very high strength values: Toughened glass is the clear choice.
- For reduction in thermal risk. Either provide thermal risk protection.
- For visual uniformity in large façades: Heat strengthened glass offers superior flatness and reduced optical distortion.
- For laminated units: Heat strengthened glass is often paired with laminates to retain structural strength when broken.
Viridian Expertise
At Viridian, we supply both heat strengthened and toughened glass to meet the diverse needs of architects, builders, and homeowners. Our experts can guide you through compliance with AS 1288 and ensure the right glass is specified for performance, safety, and aesthetics.