The Science Behind Bulletproof Glass

27 January 2022
27 January 2022, Comments Comments Off on The Science Behind Bulletproof Glass

We must begin, as we often do, with a clarification. Everyone calls it bulletproof glass, as do we because it’s so widely used, but on a technical level, there’s really no such thing as completely bulletproof glass. There will always be a bigger bullet fired from a bigger gun that can penetrate any thickness of protective glass. The more accurate term is bullet resistant glass, but we will continue to use the two names for it interchangeably. Regardless of what it’s called, what’s the science behind how it works.

First, What Bulletproof Glass is Trying to Stop: Bullets

There is a huge variety of bullets out there and an even larger variety of guns that can fire them. Below is a sampling of the more common ammunition by bullet caliber:

Handgun bullets: .22, .25, .38, .380, 9mm, .357 magnum, .40, .44 magnum, .45, 10 mm

Rifle Bullets: .223 Remington, 7.62×39 mm, .30-30 Winchester, .308 Winchester, 7.62×54R, and .30-06 Springfield.

What makes a bullet so destructive, of course, is the high velocity at which it can be fired out of a gun. Generally, handguns fire bullets at a velocity in the range of 750–1,300 FPS (feet per second). Rifles, on the other hand, are much more powerful and fire bullets at a velocity in the range of 1,900–4,000 FPS. That’s a lot of energy packed into a surprisingly small projectile, and yet it can do major damage. 

Second, How Can Glass Possibly Stop a Bullet?

Obviously, regular glass doesn’t stand a chance against any of the bullets listed above when fired from a gun. Acrylic, on the other hand, which is often used for transparent bullet resistant barriers, can stop some of the smaller bullets if it’s thick enough (1¼–1⅜ inches). But sheets of glass or acrylic can also be sandwiched together with something in-between them that helps strengthen the newly constructed “sandwich,” especially when heated up to high temperatures, which not only strengthens the glass but fuses all the layers together into something much stronger than the individual layers that make up the sandwich. 

What goes in between the layers of glass or acrylic? Any number of materials that fall into the family of thermoplastic polymers are called polycarbonates. Many industries use polycarbonate because it is known for its key characteristic, which is highly impacting resistance. This impact resistance is why it’s the material used between layers of glass or acrylic when making bulletproof glass. The more layers you add into this sandwich, the thicker (and heavier) the glass and the greater its ability to stop bullets of various sizes. This style of bulletproof glass is called glass-clad polycarbonate or GPC. 

What happens when a bullet hits a GPC bulletproof window? If it was designed to stop that particular caliber of the bullet, here’s how it goes: The outermost layer the bullet strikes first will probably be regular glass. When the bullet hits it, the glass shatters and absorbs some of the initial energy of the high-speed bullet impact by spreading it out across the surface of the glass. Then, the bullet encounters the next layer of impact-resistant polycarbonate, which greatly slows down the bullet, so much so that it no longer has enough speed to break through the final interior layers of glass. A bigger, faster bullet requires more layers to stop it with the same process repeated.

Underwriters Laboratory is the organization in charge of testing bulletproof glass and giving it a rating of how much protection it can provide, typically described as several rounds of a particular type of bullet, without failing. There are 8 different standard levels of protection provided by various kinds of bulletproof glass, which can be described as follows:

  • Level 1: Withstands a minimum of three shots from 9mm at a minimum velocity of 1,175 feet per second. A common choice for protection against small-caliber handguns.
  • Level 2: Resists at least three shots of .357 magnum soft points at a velocity of 1,250 feet per second. 
  • Level 3: Withstands a minimum of three shots of .44 magnum rounds at a velocity of 1,350 feet per second.
  • Level 4: Resists at least one shot from a .30 caliber rifle with a minimum velocity of 2,540 feet per second. Levels 1–3 are linear, but levels 4 and above describe different types of protection, not necessarily whether one is better or worse than one another.
  • Level 5: Withstands at least one full metal jacket round from a 7.62mm rifle with a velocity of at least 2,750 feet per second.
  • Level 6: Resists at least five 9mm rounds at an elevated minimum velocity of 1,400 feet per second.
  • Level 7: Withstands multiple full metal jacket rounds with 5.56 rifles at a minimum velocity of 3,080 feet per second.
  • Level 8: Resists at least five shots from a 7.62mm rifle.

At Creative Industries, we specialize in bullet resistant glass that offers either level 1 or level 3 protection. Why? Many businesses only need level 1 protection because the 9mm handgun is the most common gun used in violent crimes. But when you’re talking about banks, government buildings, and so on, then level 3 is more appropriate as it can protect against all the most common handguns. As the variety of ever more powerful guns and bullets continues to increase, so too will the bulletproof glass industry continue experimenting with new, tougher materials to stop them.

Bullet Resistant Products for a Wide Range of Applications

The added twist when we’re trying to protect businesses or organizations across the U.S. that necessarily have to interact with the public (customers and clients) is that we must provide the desired protection while at the same time still facilitating transactions and communication through the protective barrier. This is where Creative Industries really shines with its wide range of products to do that just that including the following:

  • Bullet Resistant Windows: We make more than 15 different configurations of standard bulletproof windows that serve a wide range of applications while still facilitating interactions and transactions.
  • Deal Trays: Our 13 different deal tray products provide protection when employees need to pass small items back and forth in order to complete transactions.
  • Drawers: We offer 9 styles of drawer products like the ones you’ve used at the drive-thru window of a bank. The employee extends the drawer so a customer can put things into it, then pulls the drawer in to complete the transaction, and extends the drawer again to give the customer anything they need to get back, such as a deposit receipt or cash.
  • Pass Thrus: These 11 products are larger than drawers useful when employees and customers need to pass packages of various sizes back and forth. 
  • Talk Thrus: We also make 7 different kinds of talk thrus we can add to various bullet resistant transparent barriers to facilitate verbal communication between an employee and the client or customer being served.

Greater Safety and Security with Creative Industries

All the products listed above are standard products that may or may not meet your needs. Creative Industries can also customize any type of bullet-resistant barrier, transparent or otherwise, that meets your security requirements and also fits the aesthetic of your facility. We’re eager to hear from you and discuss your needs and how we can help. Get in touch through the Contact page of our website or call us directly at 800-776-2068 to start the conversation!