Can a “Bulletproof Vest” Also Stop a Knife?

Knives and Bulletproof Vests

At the risk of sounding like a condescending ass, knives aren’t bullets. The only exception is when I butter my toast with ammo in the morning. (Image by imaspy via sxc.hu)

TLDR: Most likely not.

Bulletproof vests on walls of corpses sparked the idea for today’s topic. But before I get into that, a point of clarification.

“Bulletproof vest” is a misnomer. No vest, as this post explained, is bulletproof. That’s why it’s better to refer to that gear as a “ballistics vest,” “ballistic resistant vest,” “ballistic body armor” or some variant along those lines. I used “bulletproof vest” in the title of this post because it’s an easy way to get the point across. I suppose this makes me a hypocrite to a certain extent, which is why I write posts like this one.

Anyway. Let’s get into this. Could a ballistic resistant vest also stop a knife or other edged weapon? The answer starts with understanding how body armor works.

Body Armor is Divided into Two Distinct Categories

As the National Institute of Justice (basically the body armor guru in the States) points out, there are two types of body armor: ballistic resistant (for bullets and other projectiles) and stab resistant (for edged weapons like knives). Both of these categories try to achieve the same thing: stop something from passing through the armor. However, they achieve those goals in different ways.

Ballistic resistant armor disperses kinetic energy from a projectile, like a bullet, through a network of fibers (such as Kevlar) sort of like a speeding soccer ball getting trapped in goal netting. Depending on the level of resistance, the armor might also use hardened panels to better redirect that energy. You can watch a video detailing how this works here.

Stab resistant armor is different. It’s made of several layers of strong materials (such as Kevlar) that more or less catch the weapon as it strikes. The edge (slashing) or tip (stabbing) of the weapon is caught inside the material yet unable to make a cut. Here’s how that process works.

How Stab Vests Work

Not all stab vests work with a metal layer on top, but the idea to catch the knife in the material is the same. (Image courtesy TurtleSkin.)

Like ballistic armor, stab armor is separated into levels of resistance: I, II and III. The higher the number, the more force it can withstand.

Both Types Use Kevlar, So What’s the Difference?

Stab vest

Is this a ballistics vest or a stab vest? It’s hard to tell because the vest itself isn’t anything special. It’s just housing for the inserts that go inside. The inserts are what contain the materials that will stop a bullet or a knife. (By SGGH speak! 16:20, 3 January 2008 (UTC).SGGH at en.wikipedia [Public domain], from Wikimedia Commons)

It’s true that both types of body armor consist of strong materials like Kevlar, but it’s the way those materials are used that matters.

With a ballistics vest, energy is redirected across the armor. A stab vest is less concerned about redirecting energy, and instead allows the edged weapon to penetrate into the material (that’s a critical detail). That’s where the stab vest nestles the weapon in strong materials that the edge or point can’t completely cut through.

This is a major difference, and you might already see where it’s headed.

Because They Allow for Some Penetration, Stab Vests Aren’t Good at Stopping Bullets

Allowing for a little bit of penetration goes a long way when you’re talking about stopping a bullet. Sure, a stab vest might stop some of the lighter calibers on a good day. But the intermediate and larger calibers? Forget it.

Bottom line: Stab vests aren’t designed for the kind of energy dispersal that’s key to stopping a bullet.

And Vice Versa

The opposite is true when it’s a ballistics vest up against a knife. That type of armor isn’t designed to trap an edge or point in its fibers. Yeah, it offers a degree of protection that could prevent injury, but don’t bank on it.

The Verdict

Nope, a “bulletproof vest” most likely wouldn’t stop a knife. I wouldn’t go so far as to make an absolute verdict, because there are always exceptions. There’s room for creative license, but you might want to highlight why in the story.

How This Impacts Your Characters

UK_police_stab_vest

The setting can play a part in which type of body armor a character uses. Civilian firearm ownership is highly restricted in the UK. Police officers there typically wear stab vests, as in the photo, because the risk of being attacked with a knife is most likely. (By KRoock74 (Own work) [CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0)%5D, via Wikimedia Commons)

If you’re going to assign body armor to your characters, decide which category will be used. Match it to the threats present. For example, prison officers would opt for a stab vest because of the low risk of gunfire. Likewise, a character raiding a well-armed drug lord’s mansion would pick the ballistics vest.

This also means a character with a knife isn’t out of options when an opponent shows up with a ballistics vest, especially given the 21-foot rule. (Read more about that in The Writer’s Guide to Weapons.)


Get the Book

The Writers Guide to WeaponsThe Writer’s Guide to Weapons: A Practical Reference for Using Firearms and Knives in Fiction (Writer’s Digest Books) comes with everything but the ammo. Pick up a print or digital copy from these fine retailers:

7 thoughts on “Can a “Bulletproof Vest” Also Stop a Knife?

  1. Hello Ben!

    After finally finishing ‘Glass Eye’ over at Wattpad dot com I enjoyed checking your site. I really hate to be a bitch about minor detail, but maybe a knife be should seen for what it is.

    A knife is a versatile tool and weapon capable of slashing and stabbing aka piercing. Even a simple bouncer jacket, which is made of only one layer of kevlar, and used just as one would use cotton or nylon to craft a sweatshirt or jacket, could resist a slash with a knife or at least reduce the damage done.

    Stabbing or piercing then, needs what you did explain so well above here in the text: A multi-layered armor of different components defeating the knife by reducing the impact and entangling the blade, thereby preventing it from being driven deeper (into our body).

    IF i remember the psychology of knife-fighting and knife-attacks properly, then one can say that kevlar is certainly helpful against slash attacks, which look more intimidating and are harder to dodge, but remain actually less efficient than stabbing, thrusting or piercing. Henceforth the profession clothing of certain cooks and fishermen being reinforced with kevlar IS protective, too.

    For law enforcement, military, and armed martial arts a simple one layer of kevlar would certainly NOT suffice in any form.

    Beyond that, authors & writers who want to describe realistic or at least innovative forms of attack and combat might profit from not only reading some basics on self-defense, but actually participating in some courses by reputable & reliable instructors (greed for money and attention is not qualification enough). My own last free research involved:

    http://www.samharris.org/blog/item/the-truth-about-violence

    Liked by 1 person

    • Hi Andre,

      Thanks for reading Glass Eye! I’m happy you enjoyed it.

      There are no absolutes when it comes to guns and knives, so your point is well taken. There are times certain materials will work better than others for resisting projectiles or edged attacks. The nuances of these things would take too long to spell out in most of these posts and in my Writer’s Digest book, so I end up having to simplify the topic down to its most basic parts. Can a ballistics vest provide protection against a knife? It can, depending on the way the knife is used. Is it better than a T-shirt? You bet it is. As you say, the best way to learn about the exceptions to the rules is to experience some of this stuff for yourself. For everyone else, though, at least they have a better understanding of a subject they wouldn’t have explored much in the first place.

      If you’d like to share some of the research you’ve done for your fiction in a formal post, I’d be happy to host you. Just let me know.

      Best,

      Ben

      Liked by 1 person

      • Thank you, Ben. I agree on solid basics being a helpful summary to start with. And I repeat that I appreciate your dedication to that fact-based viewpoint PLUS the way authors can make inspiring or entertaining use of it in fiction. For now my research data is destroyed, but if I recover mature sites on protective clothing I will try to contact you. Goodbye!

        Liked by 1 person

  2. I would assume that there exist combination vests that afford some level of both ballistic, and stab resistant, protection to the wearer.

    Like

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