While the average home-owner has no need for bulletproof glass, we thought it would be interesting to explain the difference between bulletproof glass and conventional glass. The short story and the basic principle of how it works is that bulletproof glass is designed to dissipate the energy of the bullet.
Why Conventional Glass Shatters
Much in the way that you catch a fastball, bulletproof glass is constructed in such a way that it gradually slows down the bullet. Imagine trying to catch a fastball without moving your hand. It hurts right? To avoid this, you actually move your glove backwards as you catch the ball to absorb some of the energy.
To phrase this in more scientific terms without getting too deep into the physics and the math, the force exerted on your hand by the ball is directly related to the rate in which the momentum of the ball changes. The goal is to gradually slow the ball down to reduce the peak force. If the balls speed is reduced from 100 MPH to zero in .001 seconds, the force would be 10 times the force as compared to slowing the ball down over a period of .01 seconds. I know; too much information!
A glass window is fixed in a frame or sash, so for the most part it doesn’t move upon impact. When a bullet hits a conventional window, the glass can’t bend or retract so there is no way to absorb the energy. The bullet shatters the glass and continues on its path while keeping most of its momentum. This explains why conventional glass offers virtually no protection.
How does Bulletproof Glass Work?
Bulletproof glass is far different than conventional glass. It is constructed of multiple layers of polycarbonate (strong plastic) sandwiched between layers of special glass (harder than normal). The laminated assembly can be as much as ten times thicker than a standard single pane of glass, and therefore it is very heavy.
As the high-speed bullet makes contact with the bulletproof glass, its energy is quickly absorbed by the various layers. The energy is dispersed sideways through the layers of polycarbonate and glass. The bullet is slowed down to the point that it no longer has the energy to make its way through the glass.
The laminate servers a dual purpose, not only does it absorb the energy of the bullet. It also keeps the glass shards together. Much like the windshield of a car, the small pieces of glass stay together so you don’t need to worry much about flying debris.
Bulletproof Glass Video
A word of caution, there is really no such thing as 100% bulletproof glass. It should really be called bullet-resistant.