Q: Some smartphones are built with Kevlar. That’s not the same stuff that’s in bulletproof vests, is it? And how does Kevlar stop a bullet, anyway? – Dan MacDonald, London, Ont
Yep, the Kevlar in some smartphones – like the Motorola Razr HD, below – is the same material that you’d find in a bulletproof vest. Not as thick, mind you, but the material itself is the same.
Five times stronger than steel, Kevlar is an aramid fibre, which means it has heat-resistant properties and high tensile strength. Tensile strength refers to how much force is required to stretch a fibre. By contrast, elastic has a very low tensile strength, which is why it’s used to hold up your underwear as opposed to a bridge.
Kevlar’s high tensile strength means that its fibres will absorb the impact of a high-speed projectile – like a bullet – but won’t break. Since Kevlar strands are woven together, they enjoy strength in numbers. The impact of a projectile like a bullet is spread out and absorbed by the myriad individual fibres when woven into a fabric. Many layers of woven Kevlar strands come together to make a nearly impenetrable vest, or the back or body of certain smartphones. Now, the layer of Kevlar on your phone isn’t as thick as the layer in a police officer’s vest, so it’s not necessarily going to stop a bullet. But it means that a thin phone doesn’t equal a frail phone. A phone with Kevlar will take pretty much all you can throw at it.
How kevlar works in bullet proof vests:
- Individual Kevlar fibres are knitted together in a traditional woven pattern.
- The energy of the bullet is absorbed and spread horizontally across the Kevlar weave.
- By dissipating the forward momentum horizontally, the Kevlar weave effectively stops the bullet from penetrating the vest. It turns what would otherwise be an ingress into an impact.
- The end result: a big sigh of relief and probably a couple of bruised ribs. But no hole!