One-way Bulletproof Glass and Armored Cars

Bulletproof glass offers protection to those seeking safety, but sometimes individuals must respond with force and not just hide. The idea of one-way bulletproof glass has been around for some time and improved upon over the years. The objective is to stop bullets from entering from the outside but allow them to exit from the inside. This is commonly used in armored cars to protect passengers while enabling security guards to fire out of the vehicle.

Al Capone's Armored Cadillac. Photo from

The government used its first armored car in 1941 with President Franklin D. Roosevelt. After fear of a presidential assassination following Roosevelt’s “Infamy Speech,” the Secret Service used Al Capone’s recently confiscated 1928 Cadillac to transport the president. Capone had outfit the vehicle with “3,000 pounds of bulletproof armor beneath the standard body” and painted it to replicate the existing government vehicles. (Image on right taken from

How does one-way bulletproof glass work?

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 bulletproof 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.

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