While we sometimes flip flop between our use of the words “bulletproof” and “bullet-resistant,” the industry term is bullet resistant glass because it would be difficult to create a piece of glass the thickness needed to make it truly bulletproof while still maintaining visibility and communication.
There are two types of bullet resistant glass – solid acrylic and laminated polycarbonate. Solid acrylic is just as its name suggests – a solid sheet of acrylic either 1-1/4” or 1-3/8” thick depending on the level of protection required. Laminated polycarbonate is made by layering polycarbonate, a heavy-duty clear plastic, between two sheets of glass and laminating it all together. It can be ¾”, 1” or 1-1/4” thick depending on the level of protection. While a bullet will pierce the exterior glass layer of laminated polycarbonate, the inner layers absorb the bullet’s energy stopping it from penetrating through the entire piece of glass.
The newest form of bullet resistant glass is one-way bulletproof glass, commonly used in armored vehicles. One-way bulletproof glass is composed of two layers. The outside layer – on the threat side – is made of a brittle glass and the inside layer is a flexible polycarbonate. A bullet that strikes the brittle external layer first causes the glass to break inward toward the polycarbonate layer. The glass breaking absorbs some of the bullet’s energy by spreading the force over a larger area and the flexible polycarbonate stops the bullet.
Bullets shot from the inside of an armored car are able to penetrate the bullet resistant glass because they strike the polycarbonate layer first with more focused energy. The brittle glass layer then breaks outward allowing the bullet to pass through with minor energy loss.