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Kevlar – what is it?

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If you have ever used body armor, you have probably heard that your vest is made with Kevlar.

You can say that Kevlar is a distant, relative of Nylon with extreme tensile strength, which was the first “super polyamide” commercially developed and sold. DuPont is the company that developed nylon and Kevlar is also their registered trademark.

It was developed by an American chemist Stephanie Kwolek the early 1960s and was originally proposed as a lightweight replacement for steel bracing in tires. However, Modern Kevlar has a lot more applications, from sports equipment to body armor.

But how can a flexible and light fabric have so much tensile strength to stop a bullet? How is it made?

There are probably many questions that come to your mind when you hear about this synthetic material, and in this post, we are going to answer all of them. So, keep reading.

What materials is Kevlar made from?

To put it in super simple words, Kevlar is a type of synthetic plastic. Now, that does sound a little unimpressive, but knowing what Kevlar can do, we can be certain that it’s not. There are hundreds of different synthetic plastics that are made from different organic and synthetic materials and have different properties.

Kevlar is made from a chemical compound called poly-para-phenylene terephthalamide. Now, isn’t that a mouthful? Well, let’s break it down, is made by the chemical reaction of two substances, strong acids and chemical compounds containing hydrogen and nitrogen.

On a molecular level, this reaction results in the formation of super-strong inter-chain bonds between oxygen, hydrogen, carbon, and nitrogen bonds. These inter-chain bonds form bonded chains that act like small fortified rods.

So, once poly-para-phenylene terephthalamide is made, it is “spun” to make Kevlar fibers. This is done when the solution is still wet, and it allows all the strong bonded chains to be aligned in the fibers of the Kevlar while allowing the strong inter-chain bonds to act as a super glue, which keeps them together. The fibers are then weaved to make flexible Kevlar sheets or a super stiff finished material

Therefore, these bonded chains have extreme tensile strength parallel to their length, and the inter-chain hydrogen bonds add extreme tensile strength perpendicular to the chains. This is one of the reasons why Kevlar is so strong.

Is all Kevlar bulletproof?

Well, to be real, no material is completely bulletproof. Kevlar is used to make bulletproof vests, but it is actually only bullet resistant, and that is when it is tightly woven and layered.

So, in simple words, all Kevlar is not bulletproof, or bullet-resistant. I mean if you use a couple of Kevlar sheets, it probably isn’t even going to stop a 22 LR. However, when you stack the right layers of Kevlar fabric, you can stop bullets.

Typically, the higher the protection level of a bulletproof vest is the more layers of tightly packed Kevlar fibers it has. Moreover, the bullet resistance of Kevlar also depends upon the bullet that is shot.

Generally, Kevlar vests can only stop Pistol caliber threats up to a .44 magnum. To stop threats above that, and rifle threats, you would need a lot of Kevlar, which wouldn’t be practical in the form of Bulletproof vests.

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How is Kevlar use in body armor stop a bullet?

Kevlar gets the ability to stop bullets because of its molecular structure. The strong hydrogen bonds between its molecules give it an excellent tensile strength, therefore, stretching its fibers is very difficult.

In a bulletproof vest, Multiple layers of tightly woven Kevlar are stacked together. When a bullet hits the bulletproof vest, it tries to stretch these fibers, however, since they can absorb a lot of force without deforming, they prevent the bullet from breaking through.

Some fibers may break, and others stretch a little, but they absorb enough force before breaking that the bullet is stopped.

When it comes to stopping bullets the amount of Kevlar sheets used in a vest matter a lot. Level ii vests use fewer sheets and provide less protection as well. Level II Kevlar vests stop most common pistol calibers including 45 ACP, 9mm, 40 S&W, and .357. Level IIIa vests offer more protection and are denser. They can stop up to a .44 magnum.

Kevlar - what is it?
NIJ Levels of Protection.

Why is Kevlar so strong?

Did you know? Kevlar has very high tensile strength, which is approximately eight times more than the tensile strength of steel wire. For a material that is stronger than steel, it is very light weight compared to other materials. Kevlar has incredible resistance against high and low temperatures. It has a very high heat resistance and it takes about 450℃ of heat to decompose its many inter chain bonds.

Kevlar materials are also highly resistant to very low temperatures, and unlike other composite materials, it does not become brittle or at extremely cold temperatures. Kevlar is also abrasion-resistant.

These features make Kevlar an ideal material for the production of body armor for ballistic resistance and protection against sharp objects. It is strong, lightweight, flexible, and resistant to environmental factors like temperature, which is why it is used to make bulletproof Kevlar vests.

However, why is Kevlar so strong? Well, it has a lot to do with its chemical structure and manufacturing process.

Like any polymer, the chemical structure of Kevlar are arranged in a repeating manner with super-strong bonds. In Kevlar, these repeating molecular patterns form long strongly bonded chains that line up parallel with each other, increasing each other’s tensile strength.

These long parallel chains are also connected with perpendicular hydrogen bonds, which makes kevlar stronger than most natural materials on an equal weight basis.

The way Kevlar is manufactured for use in body armor also adds to its strength. Kevlar fibers are very strong on their own, however, to form a sheet, they are tightly woven. Then multiple tightly woven sheets of kevlar are stacked together, for extreme tensile strength.

Is Kevlar expensive?

For a long while, Kevlar has been the material of choice for body armor used by police officers and the military. It has high tensile strength, is lightweight and Flexible, and is very effective in stopping bullets. However, it is also quite expensive to manufacture. The making of Kevlar involves complex spinning methods, and the use of chemicals like concentrated sulphuric acid, which can be very difficult to work with.

When it comes to ballistic kevlar vests, the prices depend a lot on the level of protection as well. The higher the protection level, the more expensive the vest is. However, aside from body armor, kevlar is used for other applications as well. As a high strength material, that is also light, it has a lot of industrial applications.

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