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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:

  1. Individual Kevlar fibres are knitted together in a traditional woven pattern.
  2. The energy of the bullet is absorbed and spread horizontally across the Kevlar weave.
  3. 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.
  4. The end result: a big sigh of relief and probably a couple of bruised ribs. But no hole!

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