What is tempered glass?
Reviewed by the Skyview Auto Glass technical team — NWRD-, ASE- and DINITROL-trained technicians · Updated November 2026
Quick answer
Tempered glass is safety glass that has been heat-treated so it is stronger than ordinary glass and crumbles into small, granular pieces when it breaks. It is used for most side and back windows on cars. It cannot be repaired with resin the way a windshield can — a cracked or shattered tempered pane is replaced.
How tempered glass is made
Tempered glass is made by heating a pane of glass to a high temperature and then cooling it rapidly. The surface cools and shrinks faster than the core, which puts the surface under compression and the core under tension. That locked-in stress is what makes the glass stronger than ordinary glass.
The same stress is why tempered glass breaks the way it does. When the surface is chipped or struck hard enough to break through the compression layer, the stored tension releases all at once and the pane crumbles into small, granular pieces instead of sharp shards. That is why it is called safety glass.
Where tempered and laminated glass are used
A vehicle uses both types, each where its properties fit best.
| Glass type | Where it is used | How it breaks |
|---|---|---|
| Tempered | Side and back windows | Crumbs into small pieces |
| Laminated | Windshield | Stays in one sheet |
| Tempered | Sunroof and moonroof | Crumbs into small pieces |
| Laminated | Some newer side glass | Stays in one sheet |
Some newer vehicles use laminated side glass for sound and security. See our guide on laminated versus tempered glass.
Why tempered glass cannot be repaired
- A chip through the surface releases the tension and the whole pane crumbles.
- Resin cannot bond a pane that has already broken into granular pieces.
- A cracked tempered window is replaced, not repaired.
- A windshield, by contrast, is laminated and can take a resin repair on qualifying damage.
More questions about tempered glass
Is tempered glass stronger than regular glass?
Yes. The heat treatment puts the surface under compression, which makes tempered glass several times stronger than ordinary glass of the same thickness. It still breaks under a sharp enough impact.
How is tempered glass made?
The pane is heated to a high temperature and cooled rapidly. The surface shrinks faster than the core, locking the glass under compression on the surface and tension in the center.
Can a cracked tempered window be repaired?
No. Tempered glass crumbles when it breaks, and resin cannot bond the granular pieces. A cracked or shattered tempered pane is replaced. A laminated windshield, by contrast, can be repaired on qualifying damage.
Related guides
More in Glass types and features
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