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Flak Jackets vs. Bulletproof VestsWhat's the difference?

By Brendan I. Koerner
Posted Friday, Nov. 12, 2004, at 6:31 PM ET

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In the midst of the assault on Fallujah this week, a Reuters cameraman saw insurgents stealing scores of flak jackets from a police station, which they subsequently set on fire. What's the difference between a flak jacket and a bulletproof vest?

Today, the terms are often used interchangeably, but flak jackets weren't always considered bulletproof. Protective vests called flak jackets were first used in World War II; the word "flak" comes from the abbreviated form of the German word Flugabwehrkanone, a type of antiaircraft gun. The original flak jackets were nothing more than nylon vests with steel plates sewn inside. They were first worn by gunners in the Army Air Corps to protect them from airborne shrapnel. This early armor, however, was far too heavy for mobile ground troops.

After World War II, the jackets were reinvented for general combat use. Manufacturers of the new gear ditched the steel plates, opting for a lightweight design that featured multiple layers of dense nylon and weighed around 8 pounds. During the Korean War, when these flak jackets were first used en masse, an Army report concluded that the vests reduced the number of chest, back, and abdomen wounds by up to 70 percent.

Some improvements were made during the Vietnam War, but the design remained essentially the same: layers of nylon that shielded the body from metal fragments. Flak jackets, however, were far less effective at stopping arms fire, especially from rifles. In other words, they weren't meant to be bulletproof, just shrapnelproof—or, at the very least, shrapnel-resistant.

The big change came with the development of Kevlar. The ultra-strong fiber was first developed by DuPont chemist Stephanie Kwolek in 1965 as a way to make radial tires lighter. The company soon discovered that it was also more effective than nylon at dissipating the energy of bullets, yet comparatively light. Starting in 1975, then, new flak jackets were constructed from Kevlar; since then, rival fibers like Honeywell's Spectra have also been used in such protective gear.

The latest flak jackets don't rely just on Kevlar or Spectra, however. Like the earliest vests worn by World War II gunners, today's jackets feature pouches for the insertion of armor plates—ceramic rather than steel—which boost the gear's bullet-mitigating powers. The standard today is the Interceptor Multithreat Body Armor System, which consists of both a Kevlar flak jacket and ceramic inserts. Even without the plates in the pouches, the flak jacket is supposedly strong enough to stop a 9 mm bullet, meaning it's at least somewhat worthy of being called a bulletproof vest.

Bonus Explainer: Know someone who owes their life to a modern flak jacket? Have them fill out the 14-page application for the Kevlar Survivors' Club, sponsored by DuPont.

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Brendan I. Koerner is a contributing editor at Wired and a columnist for Gizmodo. His first book, Now the Hell Will Start, is out now.
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