Bulletproof Glass


Bullet Proof Glass!

(By, Kevin Le)

Bulletproof glass; it is used in movies, cars, buildings – just about anywhere where glass can be replaced.  Yet, for something so well known, surprisingly few people know how bulletproof glass actually works, and it is actually quite interesting.  At first glance, bulletproof glass looks like any other piece of glass – it is clear, transparent, and light can pass through it.  However, like the name implies, bulletproof glass is capable of enduring one or several rounds of gunfire depending on the thickness of the glass and what weapon is being fired at it.

Although there are many different variations of bulletproof glass, the core process is called lamination, which is what happens when multiple sheets are layered on top of each other.  Bulletproof glass is made by laminating a polycarbonate material between two sheets of ordinary glass to create a glass-like material that is thicker than normal glass (7 – 75 mm).  Polycarbonate, also known by the brand names of Lexon, Tuffak, or Cyrolon, is a type of thick, but transparent, plastic which is flexible and able to absorb large amounts of energy.  So, although the bullet will pierce the glass, the polycarbonate will absorb the rest of the bullet’s energy before it reaches the final layer of glass.

No two variations of bulletproof glass are equal.  How much energy a piece of bulletproof glass can take is determined by its thickness.  For example, a 10mm thick piece of bulletproof glass may be able to withstand a shot from a handgun, but not from an assault rifle.  There are also types of bulletproof glass that are one-sided.  This prevents the perpetrator from shooting at the victim from the outside while allowing the victim to shoot back at the perpetrator from the inside.  One-sided bulletproof glass is made by laminating a flexible sheet of material with a brittle sheet of material.  Yet, the flexible material would be on the inside, so it brings up questions as to how the person from the inside could shoot back out.  The answer lies in physics.  From the outside, when the bullet hits the brittle material, the entire surface shatters and absorbs some of the energy over a large area before the flexible material finishes the job.  However, when a bullet is shot from the inside, the bullet affects a smaller and more concentrated area, thus allowing the bullet to break through both the glass and the flexible material to strike the perpetrator.

So, while it is true that bulletproof glass can stop bullets, the way bulletproof glass is depicted in movies is slightly exaggerated.  Although the glass will stop bullets, it can only take so many rounds from the right kind of weapon before giving away.  At the moment though, bulletproof glass is crucial to places of security where people need to be protected from gunfire as well as be able to see who is firing at them.

Posted in How Things Work