Bulletproof Glass

Introduction

Bulletproof glass is a generic term we give to glass that is strong enough to resist being penetrated when it is struck with an object, including bullets fired from guns. The term bullet proof is a bit of a misnomer as “bullet resistant” would be a more accurate term. This material is used in a wide variety of applications where security and safety are of paramount concern.

Composition Bulletproof glass is typically made with a process that integrates different types of glass in a laminated configuration. The layers will alternate between soft glass types and harder configurations. The net result of this approach is that the composite glass will be more elastic than a single sheet of glass and will tend to flex when struck instead of shattering like plain glass will. The softer layers of glass are usually polycarbonates or thermoplastic recipes that are alternated with layers of tempered glass. This layered approach creates a very heavy glass composite that may be over three inches thick. In general, the thicker the glass the more able it is to withstand a shock, blow or bullet.  When a bullet strikes this material the glass will deform the bullet and flatten it out while the polycarbonate bends upon impact, thereby spreading the energy across a wider area and limiting the bullets ability to penetrate.  The fundamental characteristic of bulletproof glass is one of energy absorption.

Applications

Bulletproof glass can be found in a wide range of applications where protection, security and safety are of primary consideration. Banks, government buildings, jewelry stores and other places where money or valuables need protection are some of the most common commercial applications. The military depends heavily on bulletproof glass for protection in vehicles and as part of many weapons. One of the most visible examples of bulletproof glass in a transport vehicle is the glass bubble that covers the “Popemobile” while another bulletproof bubble is famous for the fact that it was absent from the roof of the limousine carrying President John Kennedy when he was assassinated.

Considerations

Bulletproof glass is an important and valuable safety tool. It offers protection without reducing visibility in a wide range of situations. That said, there are a few drawbacks to Bulletproof glass. Bulletproof glass that contains a polycarbonate will eventually degrade if it is exposed to solvents or UV radiation and will also become increasingly brittle as a function of time. At temperatures below -7⁰ C a direct hit on the polycarbonate material will create fragments that can become projectiles themselves. Lastly, the thicker Bulletproof glass panels will partially block light, creating a darker looking panel.