by Chris Woodford. Last updated: February 16, 2022.
If you're in the front line, in the danger zone,ducking bullets from all directions, you need all the help you can get.No-one can move fast enough to dodge a sniper's bullet, when they can't even see it coming. There's only one way to protect yourself: place a barrier in front of your body thatwill dissipate a bullet's energy. That's the basic idea behindbulletproof glass. Let's take a look at how it works!
Photo: There's no such thing as totally bulletproof glass.In this controlled test carried out by the US Air Force, a very powerful AK-47 assault rifle has shattered a piece of armored glass to smithereens.Picture by Gary Emery courtesy of the US Air Force.
- Why ordinary glass shatters
- How bulletproof glass works
- How do you make bulletproof glass?
- Where is bulletproof glass used?
- Standards for bulletproof glass
- Who invented bulletproof glass?
- Find out more
Why ordinary glass shatters
Photo: You have to absorb a ball's kinetic energy (energy of movement) to bring it to a halt and catch it successfully. Picture by John Collins courtesy of US Navy and Wikimedia Commons.
If you've ever caught a fast-moving baseball or cricket ball, you'llknow the trick is to move your hand back and stop the ball gradually so you reduce its energy very slowly. That reduces the forceon your hand so the catch hurts less. Putting it more scientifically,the force the ball exerts on your hand is equal to the rate at which the ball's momentum changes.So if you change its momentum slowly, by bringing it to a halt gradually,the force you feel is reduced. Let's say you stop a ball nearly instantly in half a secondand you feel a hefty smack as your hand absorbs the impact.Now suppose you could replay the moment and take two seconds to stop the ball instead.This time, taking four times longer to bring the ball to rest, your hand would feelonly quarter as much force—so the ball would hurt you much less.
Photo: Normal glass offers little protection against bullets.When a bullet strikes a pane of glass, the bullet's energy pushes against the glass, making fractures radiate out from the point where the bullet hit along lines of weakness. This is what makes glass shatter into huge shards.Glass damaged like this adds an extra element of danger: if the bullet doesn't kill you, the glass just might.Picture by Bennie J. Davis III courtesy of the US Air Force.
Unlike your hand, a piece of glass can't move. If someone fires a bullet at an ordinary piece ofglass, the glass can't bend and absorb the energy very gradually. So it simply shatters and the bullet carries on through with hardly any loss of momentum. That'swhy ordinary glass offers no protection against bullets: it is completely ineffective at slowing them downand absorbing their energy.
Animation: Why glass shatters. Metals (left) have a crystalline structure: the atoms (red) inside are arranged in regular, repeating patterns. Apply a force (with something like a bullet or a hammer blow), and the planes of atoms simply shift pass one another, so the metal twists and bends to soak up the energy. Glass (right) is different. It has an amorphous (irregular) structure. Its atoms (blue) can't easily shift aside when a force is applied and the incoming energy has nowhere to go, so it splits the whole material apart. That's why metals bend, while (ordinary) glass shatters.
How bulletproof glass works
"Bulletproof" glass is very different to ordinary glass. More correctly calledbullet-resistant glass (because no glass is totally bulletproof), it's made frommultiple layers of tough glass with "interlayers" of various plastics.Sometimes, there's a final inner layer of polycarbonate (a tough type of plastic) or plastic film to prevent "spalling" (where dangerous shards of glass or plastic splinter off following the impact of a bullet). This sandwich of layers is called a laminate. It can be up to ten times thicker than a single pane of ordinary glass and it's usually very heavy.
When a bullet strikes bulletproof glass, its energy spreads out sideways through the layers. Because the energy is divided betweena number of different pieces of glass and plastic, and spread over a large area, it is quickly absorbed.The bullet slows down so much that it no longer has enough energy topierce through—or to do much damage if it does so.Although the glass panes do break, the plastic layers stop them flyingapart. Think of bulletproof glass as "energy-absorbing" glass andyou'll have a good idea how it works.
Photo: Top: Ordinary glass shatters and does nothing to stop the passage of a speeding bullet. Bottom: Bulletproof glass shatters too, but the layers of plastic sandwiched between the layers of glass absorb and dissipate the bullet's energy. If it does manage to penetrate through the glass, it will be greatly slowed down and it will do much less damage.
How do you make bulletproof glass?
Traditional bulletproof glass is made from alternating layers of glass (typically 3–10mm or ⅛–⅜in) and plastic, where the plastic is simply a thin film of polyvinyl butyral (PVB) (around 1–3mm or 30–90 mils thick). Newer, stronger kinds of bulletproof glass use a sandwich of glass and plastic made of acrylic glass,ionoplast polymers (such as SentryGlas®),ethylene vinyl acetate,or polycarbonate,with the thick glass and plastic layers separated by thinner films of various plastics, such as PVB or polyurethane.
Artwork: Bulletproof glass is essentially a multi-layer sandwich of glass and plastic, butthere are many different ways of arranging the ingredients. In this example, there are multiple layers of glasswith thin plastic interlayers binding them together and one thick layer of polycarbonate—but manyother arrangements are possible.
To make simple PVB-based bulletproof glass, the thin PVB film is sandwiched between the thicker glass to make a laminate, which is heated and compressed so the plastic melts and begins to bond to the glass. Often this process happens in a vacuum to prevent air becoming trapped between the layers, which makes the laminate weaker and affects its optical properties (distorting the light that passes through). The unit is then fully "cooked" at a much higher temperature (up to about 150°C or 300°F) and pressure (up to about 13–14 times normal atmospheric pressure) in an autoclave (a kind of industrial pressure cooker). The main difficulty with the process is ensuring that the plastic and glass layers stick together properly with no air trapped between them, and ensuring the autoclave's heat and pressure doesn't distort the plastic so it becomes difficult to see through. (You can read more about the manufacturing process in US Patent: 5,445,890, listed in full in the references below.)
Where is bulletproof glass used?
Photo: This bulletproof armor withstood the impact ofa .30 caliber armor-piercing bullet fired from 23 m (25 yards) awayusing a Russian M-44 sniper rifle. Picture courtesy of US Air Force.
Bulletproof glass comes in all shapes and sizes to give different levels of protection in different situations.You're most likely to find it in places like banks, where the tellers typically sit behind thick bulletproof windows and use bulletproof drawers to exchange paperwork and money with customers.Generally speaking, the thicker the glass and the more layers it has, the more energy it can absorb and the more protection it will give. Basic bulletproof glass ranges from about 3cm (1.185 in) to 4cm (1.59 in) thick, but it can be made twice this thick if necessary.
The only problem is, the thicker you make bulletproof glass the heavier it becomes. That may not be a problem in a bank, but it's certainly a consideration when you're trying to bulletproofa president's car or a "Popemobile".Making bulletproof glass thicker also makes it slightly more opaque, because light struggles to get through all those extra layers. That can cause difficulties if it impairs the driver's visibility. Rap artist Buster Rhymes ran into problems in 2007 when police stopped his SUV (with its 5cm/2in-thick bulletproof glass) "for having excessively tinted windows" (only 70 percent light transmission).
Standards for bulletproof glass
Different standards exist in different parts of the world. In the United States, the effectiveness of bulletproof glass is typically compared using NIJ (National Institute of Justice) Standard 0108 for Ballistic Resistant Protective Materials (September 1985), which lists seven kinds of armor broken into five main types (Types I, II-A, II, III-A, III, IV, and Special). The highest classification, Type IV, must be able to cope witha single hit from a 30-caliber armor piercing rifle with a bullet mass of 10.8g and measured velocity of 868±15m/s. In the UK, the relevant British Standard is BS EN 1063:2000, which compares nine different types of glass (BR1 for handguns and rifles, BR2–4 for handguns, BR5–7 for rifles; and SG1–2 for shotguns). Elsewhere in Europe, that's equivalent to CEN 1063.
Chart: You need thicker glass to stop bullets with higher velocities and energies. This chart compares the effectiveness of bulletproof glass rated BR1–7 on the standard EN/CEN 1063. BR1 would typically be around 13–15mm (0.5–0.6in) thick; BR7 would be more like 75–85mm (3–3.5in)—roughly six times thicker.
Who invented bulletproof glass?
Modern bulletproof glass is simply a variation on laminated safety glass, and that was invented by a French chemist named Édouard Bénédictus (1878–1930),who took out a patent on the idea in 1909. His original version used celluloid (an early plastic)sandwiched between two sheets of glass. The idea of using polyvinyl plastics in laminated glassdates from 1936, when it was first proposed by Earl Fix of the Pittsburgh Plate Glass Company.Popular Science was flagging up the possible use of bulletproof glass in armored policebuses the following year (in its April 1937 issue).If you wanted "bulletproof glass" before the 1930s, you had to resort to using very thick ordinary glass:gangster Al Capone's 1928 Cadillac—one of the first ever bulletproof vehicles—didn't have modern laminated safety glass but inch-thick ordinary glass.
Artwork: Earl Fix's idea was to sandwich polyvinyl acetal resin (PVA) between two layers of glass.Artwork from US Patent 2,045,130: Safety Glass, courtesy of US Patent and Trademark Office.
Find out more
On this website
- Glass: How ordinary glass works—and why it's not what it appears to be!
- Composites and laminates: How to make amazing new materials by combining ordinary old ones.
- Energy-absorbing plastics: Plastics that suddenly change form to protect things by absorbing impacts.
- Kevlar: An introduction to one of the world's most versatile protective materials.
- 'Bulletproof' Review: Americans and Their Guns by Teo Bugbee. The New York Times, October 28, 2021. A chilling documentary explores how US schools have been changed by recent shootings.
- Out of Tragedy, a Protective Glass for Schools by Claire Martin. The New York Times, December 27, 2014. Could an afforable new reinforced glass delay entry to buildings long enough to prevent mass shootings in future?
- Graphene Proves to Be Superman of Bullet Proof Materials by Dexter Johnson. IEEE Spectrum, December 4, 2014. Graphene can dissipate a bullet's energy better than steel.
- Who, what why: How many buildings have bullet-proof windows: An article from BBC News, 17 November 2011, which introduces the idea of bullet-resistant glass and looks at how bulletproof windows are used in high-security buildings (such as the White House).
- Road Warriors by Craig Peterson, Popular Science, March 1991. A slightly dated but still very interesting article about the various cunning features of armor-plated cars.
- School Guard Glass demonstration: Testing a new-type of safety glass designed to help schools resist shooting attacks.
- Armored glass demonstration: A fantastic and very persuasive demonstration by Labock Technologies (6 minutes). It's absolutely amazing to watch a sledgehammer bouncing straight back off glass for two-solid minutes!
- Bulletproof glass demonstration: Watch how bulletproof glass behaves in actual firearm tests by BP-Glass. As you watch this video, notice how the tester handles the glass planes: you can clearly see their thick, laminated construction as he reaches down and tilts them.
- US Patent: US20100024692A1: Blast and impact resistant window pane systems: by Zvika Bar (Oran Safety Glass), December 2, 2014. Describes cutting-edge explosive-resistant glass.
- US Patent: 5,445,890: Bullet-resistant glass/glass, glass/plastic, and plastic/plastic laminate composites: by Charles E. Bayha and H. Arne Sudlow (Resikast Corporation), June 6, 1994. Contains a good, clear description of how bulletproof glass/plastic laminates have traditionally been made (briefly summarized up above) and an alternative, novel method proposed by the inventors.
- US Patent 2,045,130: Safety Glass: by Earl Fix (Pittsburgh Plate Glass Company), June 23, 1936. The first patent for laminated safety glass using a polyvinyl acetal resin sandwiched between two sheets of glass.
- Laminated glass: technical FAQs: Some useful questions and answers from DuPont.
- [PDF] US Department of Justice National Institute of Justice Ballistic Resistant Protective Materials NIJ Standard 0108.01
- British Standards BS EN 1063:2000 and CEN 1063: A basic summary from Wikipedia.
How does the bulletproof glass work? ›
Bullet resistant glass, on the other hand, is made of multiple layers laminated together, typically with a thin layer of polycarbonate or another glazing material. That laminating process holds the layers of glass together even when there's an impact that causes fracturing, like that from a bullet.How is bullet proof glass so strong? ›
Bullet-resistant glass is constructed using layers of laminated glass. The more layers there are, the more protection the glass offers. When a weight reduction is needed 3mm of polycarbonate (a thermoplastic) is laminated onto the safe side to stop spall.Does bulletproof glass work both ways? ›
There is also one-way bullet-resistant glass available, which has one side able to stop bullets, while the other side allows bullets to pass through it unaffected. This gives a person being shot at the ability to shoot back.Is bulletproof glass completely bulletproof? ›
About “Bullet Proof” Glass
However, this is a misnomer, since no material can completely protect against all types of bullets. No matter how well-designed the material is, or how high its protection level, the glass will eventually give way to a persistent ballistic attack.
Bottom: Bulletproof glass shatters too, but the layers of plastic sandwiched between the layers of glass absorb and dissipate the bullet's energy. If it does manage to penetrate through the glass, it will be greatly slowed down and it will do much less damage.Is bullet proof glass easy to break? ›
Bulletproof glass (known more accurately as ballistic glass) is designed to absorb the force of a bullet rather than breaking apart. If you're determined to break through the glass, you can do so by shooting the glass multiple times in the same location or by shooting the glass with a high-powered rifle.Can a hammer break bullet proof glass? ›
Polycarbonate is stronger than acrylic so it resists firmly even against powerful rifles. So you can't break such glass with a sledgehammer or rock.What material can stop a bullet? ›
Bullet-resistant materials (also called ballistic materials or, equivalently, anti-ballistic materials) are usually rigid, but may be supple. They may be complex, such as Kevlar, UHMWPE, Lexan, or carbon fiber composite materials, or basic and simple, such as steel or titanium.What can stop a bullet? ›
- Steel. Steel bulletproof materials are heavy duty, yet at just a few millimeters thick, extremely effective in stopping modern firearm rounds. ...
- Ceramic. ...
- Fiberglass. ...
- Wood. ...
- Kevlar. ...
- Polyethylene. ...
Diamond A2Z Blades Cuts Steel, Concrete & Bullet Proof Glass - Belts And Boxes.
How long does bullet proof glass last? ›
Ballistic framing is as equally important as ballistic glass and should be considered during the design phase. With proper maintenance, bulletproof glass has a life span of up to twenty years.Can spark plugs break bullet proof glass? ›
There is no such thing as bulletproof glass. More to your question, yes, any piece of a spark plug including the ceramic insulator can breach impact resistant glass. In fact, just about anything can breach the stuff depending on your patience and your precision in hitting it in exactly the same place.How many bullets can bulletproof glass stop? ›
As identified by UL 752 standards, the highest level of bulletproof glass historically available has been Level 8, which is made to withstand five rounds from a 7.62mm rifle allowing for no penetration of the bullet and no glass spall.Can bulletproof glass stop a 50 cal? ›
The latest lightweight armoring and bulletproof glass can offer a level of protection that can make sure your vehicle remains unimpeded by bullets even from a 50 caliber round.How many bullets can break bullet proof glass? ›
A level 5 bulletproof glass is able to withstand at least 1 shot of a 7.62 rifle mm round. There was a time when this indicated a class of full-power military main battle rifle cartridge. Level 8 protection means that the glass can deflect at least 5 shots from a 7.62 mm rifle.Can you drive a car through bulletproof glass? ›
Yes, the installation of bulletproof glass in private cars is entirely legal, and anyone can install bulletproof glass for protection in their vehicle (we recommend professionals who can properly seal and install the Armormax® materials).Can bullet proof glass broken by AK-47? ›
A projectile fired from a rifle, such as the AK-47 or the Nato rifle G3, has a lower speed of up to thousand meters per second. This means: Glass breaks faster than the speed of the projectile. Therefore, the breaks in the glass are ahead of the projectile.Is bullet proof glass tornado proof? ›
Bullet Proof Glass Has Its Limits
While some polycarbonate products carry UL-verified ratings for forced entry, blasts, and even gale-force winds, these are forces an order of magnitude milder than a tornado.
Why do police cars not have bulletproof windows? It's expensive and most police departments have limited budgets. Uparmoring adds some weight to the vehicle. Bulletproof windows that still have power window functionality and go up and down are even more expensive and police need to be able to lower their windows.What is the strongest glass? ›
- Toughened (tempered) glass: This kind of glass is recommended for safety purposes. It's manufactured by use of controlled thermal or chemical treatment processes. ...
- Laminated Glass: This kind of glass tends to hold together when it's shuttered and stays in the frame. ...
- Plate Glass:
Can bullet proof glass stop an arrow? ›
Yes an arrow (or crossbow bolt) can pierce through some bullet proof vests.Can aluminum foil stop a bullet? ›
Aluminum armor can deflect all the same rounds from small-caliber weapons as traditional bulletproof glass. But while traditional bulletproof glass warps, fogs, or spiderwebs when shot, transparent aluminum remains largely clear. It also stops larger bullets with a significantly thinner piece of material.Can magnets stop a bullet? ›
Typically, no. Most bullets aren't ferromagnetic – they aren't attracted to magnets. Bullets are usually made of lead, maybe with a copper jacket around them, neither of which sticks to a magnet. These magnets made a bullet tumble on Mythbusters, but didn't change where it hit the target.What is the cheapest bullet proof material? ›
It is the most cost-effective and convenient option for bulletproofing walls.
In fact, according to The Atlantic, not removing bullets is a very common practice, and many surgeons will not attempt to remove a bullet that is not creating a problem due to its location. Often, the justification is that removing the bullet will cause additional health issues and damage.Will bullets go through water? ›
bullets can travel 60 meters through water or penetrate 2 cm of steel through 17 meters of water.Can a cast iron skillet stop a bullet? ›
Unfortunately, even a 9mm pistol can easily blast a hole through a cast-iron skillet. However, two skillets can stop pistol rounds, so do with that what you will. A cast iron tub might do the job if it were positioned so you could hide behind it, especially if you could fill it with water.Can you break bullet proof glass with sound? ›
This must be impossible, even for lady Castafiore with her earthquake voice. For a glass to break by sheer sound you need to produce a tone equal to the glass's natural frequency - the frequency at which a body vibrates with the least amount of energy.How thick does glass have to be to be bulletproof? ›
Bulletproof glass ranges from 0.25 inches to 3.5 inches and as the thickness increases, so does the weight. This is critically important to consider when designing and building structures. Bulletproof glass ranges in levels of protection from UL 1 to 10.How much is bullet proof glass price? ›
The cost of a bulletproof window ranges from $150 to $800 per square foot depending on what bullets are to be stopped, whether the window is opening, how intricate the design is, and the size of the window.
What shatters glass easily? ›
Yes, a spark plug! If you have a child trapped in your car or truck, having a spark plug on hand is perfect. The ceramic of the spark plug when hit with a hammer or other blunt object can pierce and even shatter tempered glass.
Spark plugs instantly break windows when thrown at the glass with sufficient force because they are generally made of aluminum oxide ceramic or porcelain, which concentrates a tremendous amount of energy at a single focal point on the glass.Can a sniper shoot through bulletproof glass? ›
Mostly used in the military as sniper rifles, no consumer-grade bullet-resistant system will stop a . 50-cal rifle bullet, which requires Level 10 bulletproof glass (usually three or more inches of polycarbonate plastic, which equates to almost half a foot of tempered glass).What is the most bullet proof metal? ›
In the end, titanium is bulletproof for the most part against bullets fired from guns that one would likely find on the shooting range, on the street or on the hunt in the mountains. Most guns legally bought and owned by individuals will likely not penetrate titanium.How thick is level 4 bulletproof glass? ›
Total Security Solutions' Level 4 bulletproof glass is a 4-ply combination of glass and polycarbonate that can be manufactured 1-1/2” thick. The framing system for the glass has a total extrusion of 3” x 5-1/2”.Do bullets go straight through glass? ›
The biggest factor in taking a shot through glass is the angle of obliquity, or basically, how perpendicular the bullet is to the glass. Shots that can be taken at an angle of obliquity less than 15 degrees are preferred. At any angle greater than 15 degrees the bullet will generally start to yaw and be deflected.What can destroy bullet proof glass? ›
Shoot an explosive round to break multiple layers of thick bulletproof glass. As their name suggests, military-grade explosive rounds detonate on impact and will shatter the object they're fired into. This type of super high-power ammunition will break through even the thickest 5-pane bulletproof glass.Can bulletproof glass stop AK-47? ›
At 1-inch thick, this type of glass can stop a bullet fired from an M16 or AK-47. This is why glass-clad polycarbonate is used in dangerous outdoor scenarios, including areas prone to explosions, dangerous weather, or other high-impact intrusions.Can a bullet go through water? ›
Typical bullets can travel just a few feet through the water before they're slowed to a stop. CAV-X bullets can reportedly travel 60 meters underwater, and can go through 2 centimeters of steel fired from 17 meters away, indicating that it could even be used to penetrate submarines.Can a car window withstand a bullet? ›
In general, vehicle side windows are made from tempered glass, which, if broken, breaks into relatively safe, small pieces, rather than shards. Tempered glass is not bullet-resistant.
Does a bullet sink in water? ›
Water is 800% more dense than air, so unlike a bullet fired above the surface, once the bullet hits the water it immediately begins slowing down, the Science Channel explains. And instead of barreling towards Wahl, the bullet slows and falls to the bottom of the pool.