How does one way bulletproof glass work?

Question

How does one way bulletproof glass work?

In: 541

Answer 1

There are basically three layers to a one way bullet resistant glass:

* A hard but brittle outer layer that’s very resistant to compressive force (push together forces) but not very resistant to tensile/shearing forces (pulling apart/cutting). In modern bullet resistant glass that’s various acrylics.
* A resin binding the inner to the outer layer.
* A softer flexible backing material that provides structural strength. Typically Polycarbonates.

So when the glass is fired at from the outside the outer layer is compressed against the inner layer, distributing the force over the inner layer. When fired at from the inside the inner layer is cut through by the bullet and the brittle outer layer is blasted off since there is no backing holding it together.