Tempered glass

Chemically the same soda-lime glass, heated to near softening and then chilled fast so the surface is locked in compression — a crack cannot start until that compression has been overcome, which is why it is four to five times stronger. It cannot be cut or drilled afterwards; any breach of the surface releases the stored energy and the whole pane dices into blunt fragments, which is the point for car and shower glass. It also fails spontaneously years later from nickel sulfide inclusions, which is a known and unavoidable low-rate defect rather than a fault.

Properties

Density

2,500 kg/m³ — 2.50 g/cm³

Tensile strength

120–200 MPa

Young's modulus

70 GPa

Thermal conductivity

1 W/(m·K)

Hardness

5.5 Mohs

Thermal expansion

9 µm/(m·K)

Floats in water

No

Magnetic

No

What it is used for

• Car side and rear windows
• Shower screens and glass doors
• Phone screen protectors
• Balustrades and shelving

How it compares

Does it rust?

Tempered glass contains no iron, so it cannot rust. Whether it degrades depends on the material, not on oxidation.

Is it magnetic?

Tempered glass is not a metal and has no ferromagnetic response.