How Is Bulletproof Glass Made?

There are many applications for bulletproof glass, including fiberglass panels, barriers, doors, windows, and more. Bulletproof glass is manufactured in different materials and thicknesses to meet particular protection needs. To ensure consistency for all bulletproof glass products, a standard rating system has been adopted by bulletproof glass manufacturers. Protection ranges from Level 1 to Level 8, with Level 1 offering the lowest level of protection.

What Is Bulletproof Glass Made Of?
Many resins can be incorporated into bulletproof glass, but the most common and effective materials are glass, acrylic, and/or polycarbonate bonded together with PVB adhesive.

Acrylic is typically used as a single-layer bulletproof glass for Level 1 protection in low-risk situations for commercial companies. It offers excellent clarity, with high structural stability that provides adequate protection from projectiles and a small number of 9mm bullets.

Polycarbonate is a readily-available polymer valued for its exceptional impact resistance. It can be used in single sheets or bonded with glass layers to produce a thicker, more durable bulletproof panel. As another option, PVB is a rugged, flexible, and ductile thermoplastic resin that becomes transparent during the heat treatment that bonds it with glass, making it an ideal bonding agent.

Bulletproof glass is manufactured using a wide variety of materials and methods. For lightweight bulletproof panels, a single layer of acrylic may suffice. It is important to note that thicker materials will occlude light and compromise the transparency of the material. In addition, thicker materials tend to be heavier, which can affect users’ ability to install and maintain the glass. For practical purposes, many bulletproof glass manufacturers combine layers of glass and polymer to optimize the weight, clarity, and level of protection.

When selecting the right bulletproof glass for your application, it is therefore important to consider your needs carefully. Maximum protection is not necessary for every bulletproof glass application. A thick, heavy bulletproof glass may be ideal for a police station, for example, but not necessary for a gas station. The ideal bulletproof glass will balance your protection level and practical needs, while meeting your project budget.

How to Make Bulletproof Glass
Every manufacturer uses different methods to create their own brand of bulletproof glass. Fundamentally, the process involves laminating glass, polycarbonate, or acrylic with a thin layer of PVB film, a technique known as glazing. The thicker the layers, the greater the ability to withstand a bullet. A stronger or larger bullet like a rifle bullet will expend significantly more force than a smaller bullet from a 9mm, so a correspondingly thicker layer of glazed material is needed to withstand the rifle bullet’s force. Manufacturers will laminate glass as thin as 21mm thick up to 70mm, depending on the particular needs of the application and standardized testing requirements.

How Does Bulletproof Glass Work?
Bulletproof glass works by absorbing the force exerted by a moving bullet. The larger and faster the bullet, the greater the force it will exert on the glass upon impact. By layering panels of glass, acrylic, or polycarbonate, manufacturers provide a surface material that will dissipate a significant amount of the bullet’s force. As the bullet hits each layer of material, the force dissipates further, until the bullet is either stopped or emerges from the other side of the glass at a much slower speed. Even if the bullet pierces several layers, the barrier will have absorbed a significant amount of the bullet’s force, slowing it and making it less dangerous to individuals behind the glass.

It is important to note that although appropriately rated bulletproof glass can reduce the force of bullets of a certain caliber, its effectiveness wanes with each successive impact. For this reason, while it is clearly more effective than untreated glass, it cannot be relied upon to completely stop all bullets. For optimal protection from repeated high-caliber impacts, manufacturers turn to thicker acrylic and polycarbonate layers.

To ensure that bulletproof glass is able to stop bullets without breaking, manufacturers test to standards set by Underwriters Laboratories (UL), a globally recognized independent developer of safety standards and certifications. As an OSHA-authorized organization, UL has established the most commonly used standards and ratings for bulletproof glass manufacturing based on a variety of factors, including:

• Glass material and properties
• Amount of impacting force of the projectile material
• Number of impacts

UL’s testing methodology allows manufacturers to engineer bulletproof glass to meet the following ratings:

• Level 1. Level 1 bulletproof glass is designed to withstand a minimum of three 9mm bullets from small-caliber handguns with a minimum velocity of 1,175 f/s.
• Level 2. Level 2 glass can handle three or more impacts from larger handguns with .357 magnum soft-point bullets that travel at a velocity of 1,250 f/s.
• Level 3. Level 3-rated bulletproof glass is capable of withstanding at least three shots from .44 magnum bullets at 1,350 f/s.
• Level 4. Level 4 bulletproof glass must be able to withstand a single bullet from a .30 caliber rifle traveling at a minimum of 2,540 f/s.
• Level 5. At Level 5, bulletproof glass is designed to take at least one full metal jacket (FMJ) bullet from a 7.62mm rifle at a speed of at least 2,750 f/s.
• Level 6. Level 6-rated bulletproof glass is engineered to improve upon Level 1 rated glass and can handle a minimum of five 9mm bullets at a minimum speed of 1,400 f/s.
• Level 7. Level 7-rated glass is engineered to handle multiple impacts from FMJ bullets fired by a 5.56 rifle at a minimum of 3,080 f/s.
• Level 8. The highest protective rating under UL standards, Level 8 bulletproof glass must be able to withstand a minimum of five impacts fired by a 7.62 mm rifle.

UL ratings for bulletproof glass can be subdivided into two main categories. Levels 1 – 3 are typically grouped together. They encompass lower-level protective glass where the aim is to safeguard employees against minor crime that typically involves handguns. Levels 4 – 8 are reserved for operations where rifles could be in use, such as military installations and certain government facilities.

How Is Bulletproof Glass Tested?
UL outlines specific testing methods based on the glass material and intended use. Bulletproof glass testing generally involves firing a bullet appropriate to the Level rating at a bulletproof glass test sample. A piece of corrugated cardboard is placed behind the test sample to gauge the frequency and severity of impacts from bullets and shrapnel passing through the glass.