Short answer: Tempered glass, also called toughened glass, is glass heated and then cooled fast to make the surface strong. It is several times stronger than ordinary annealed glass. It breaks into small granular pieces and cannot be cut after tempering.
What two sources say about Tempered glass
| Source page | Publisher | What the page says |
|---|---|---|
| Toughened glass | Wikipedia | Tempered glass is heated to about 620 C and cooled quickly with air, or treated chemically. It is about four times stronger than annealed glass and breaks into granular bits. Cutting or grinding must be done before tempering. |
| How is tempered glass made? | Scientific American | Glass is cut, inspected, washed, heated to about 620 C and quenched with high-pressure air. The outside ends up in compression and the core in tension, so it breaks into small, less harmful pieces. |
Key points
- The glass is heated to about 620 C and quickly cooled with air. [1, 2]
- Quenching leaves the surfaces in compression and the interior in tension. [1, 2]
- It is several times stronger than annealed glass. [1, 2]
- It breaks into small granular pieces rather than large sharp shards. [1, 2]
- Cutting or grinding must be done before tempering. [1]
- It can still break spontaneously, for example from nickel sulfide inclusions or edge damage. [1]
Tempered glass compared with Annealed glass
| Aspect | Tempered glass | Annealed glass | Source |
|---|---|---|---|
| Strength | About four times stronger | Baseline strength | [1, 2] |
| Breakage | Small granular pieces | Large sharp shards | [1, 2] |
Where sources differ
Tempered and toughened mean the same thing. Heat-strengthened glass is different. Chemical tempering also exists, so confirm the method.
Questions to ask a supplier about Tempered glass
- [ ] Is the glass fully tempered or heat-strengthened?
- [ ] Which standard does it meet?
- [ ] What is the thickness and edge finish?
- [ ] Are holes or notches done before tempering?
- [ ] Are there roller wave or distortion limits?
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Sources: [1] Wikipedia, fetched 2026-11-12; [2] Scientific American, fetched 2026-11-12. As of 2026-11-12. General information, not legal, customs or tax advice. Wording is paraphrased from the pages linked; your written quote and contract govern.