Aramid fibre (Kevlar)

At 3000-3600 MPa it is stronger in tension than all but the very best steel wire, at a fifth of the density — and tension is the only direction it is strong. An aramid fibre has almost no compressive strength, so a Kevlar laminate that stops a bullet folds easily under a bending load and is usually paired with carbon fibre for that reason. It does not melt; it decomposes above about 450 °C, which is why it survives brake temperatures. The modulus quoted here is the high-modulus Kevlar 49 type; the tougher Kevlar 29 used in armour is nearer 70 GPa, and both have a slightly negative axial expansion, contracting as they warm.

Properties

Density

1,440 kg/m³ — 1.44 g/cm³

Tensile strength

3000–3600 MPa

Young's modulus

112 GPa

Floats in water

No

Magnetic

No

What it is used for

• Body armour and stab vests
• Cut-resistant gloves and sleeves
• Composite reinforcement in canoes and drone frames
• Brake pads and clutch facings

How it compares

Does it rust?

Aramid fibre (Kevlar) contains no iron, so it cannot rust. Whether it degrades depends on the material, not on oxidation.

Is it magnetic?

Aramid fibre (Kevlar) is not a metal and has no ferromagnetic response.