BrainStuff Classics: How Effective Are Bulletproof Vests?

Bulletproof vests have certainly saved lives, but exactly how bulletproof are they? Learn what they're made of and how they can fail to protect wearers in this episode of BrainStuff, based on this article: https://science.howstuffworks.com/how-bulletproof-are-bulletproof-vests.htm

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Episode Transcript

Speaker 1 (00:01):
Welcome to brain Stuff, a production of iHeartRadio. Hey brain Stuff,
Lauren vogelbomb here with a classic episode from our archives.
Today's gets into the science and history behind bulletproof vests,
how they work and when they don't work so well,
Hey brain Stuff, Lauren Vogel bomb here. Bulletproof veests have

(00:25):
saved plenty of lives, but this gear isn't perfectly well
bulletproof in all situations.

Speaker 2 (00:30):
So exactly how well do they work? And do bulletproof
vests degrade over time? Can they fail? Let's look at
a bit of history. Early bulletproof vests were mainly made
from polyperiphenline tarphalamide, better known as kevlar. It was invented
by Stephanique Follack, a chemist working for DuPont in the
early nineteen sixties. DuPont had already invented nylon and spandex,

(00:53):
and was on the hunt for the next generation of
high performance fibers. Synthetic fibers are created with polymers molecules
composed of repeating subunits, effectively creating a linked chain of
molecules that are more than the sum of their parts.
What Kolk discovered would eventually become kevlar and would see
application in tires, racing sales, and bulletproof vests. Bulletproof vests

(01:15):
today are made from polyethylene fibers, a popular plastic polymer
seen in nearly everything we use, grocery bags, toys, plastic
trash bins, and so on. Polyethylene fibers, or pe as
it's called, are woven in layers to form the guts
of protective vests that are cheaper and stronger than kevlar.
In nineteen eighty nine, a company called Allied Signal developed

(01:36):
a competitor for kevlar and called it Spectra Shield. Originally
used for sailcloth, this polyethylene fiber is now used to
make lighter, yet stronger material for use in bulletproof vests
alongside the traditional kevlar. According to a manufacturer of bulletproof vests,
the layers inside a vest are designed to reduce the
velocity of a round to a point below the speed

(01:57):
of sound. At roughly this point, the fibers can have
time to react to the bullet and exert their toughness,
of their strength, and how much they'll bend before they break.
The more layers, or the greater the density of the
weaving of those layers, the greater the toughness of the fibers,
and the more capable they are of stopping a bullet.
Most pistols fire bullets at velocities that are just slightly

(02:18):
above the speed of sound. A bullet from a nine millimeter,
for example, travels at around nine hundred and eighty feet
per second. That's about three hundred and eighty meters per second.
The speed of sound is around one thousand, one hundred
and twenty feet or three hundred and forty meters per second. Thus,
a good vest doesn't need to work too hard to
bring a nine millimeter bullets velocity down to a point
where it can make use of the toughness of its fibers,

(02:40):
and slugs from shotguns travel even slower, so they are
relatively easy to stop as well. A rifle bullet, however,
is another matter, entirely depending on the grain and quality
of the propellant. A bullet fired from an AR fifteen
travels roughly three thousand, three hundred feet per second. That's
about one thousand meters per second, which is nearly three
times the speed of sound. It'll take a far greater

(03:02):
density of ballistic fiber to stop that bullet. Most vests
designed to stop rifle bullets are backed up with high
density insert plates made from ceramics and polyethylene that break
up a bullet into pieces and capture it. Vests without
those plates would likely fail to capture a rifle bullet.
The material of the vests themselves is also prone to
break down for various reasons. Kevlar, for instance, degrades when

(03:25):
exposed to salt such as the salt and human sweat.
The longer a person exerts themselves while in a bullet
proof vest made of kevlar to the tune of years,
the greater the likelihood of failure. Vests made from polyethylene
will also break down over time when exposed to UV light.
Manufacturers say that there's about a five year lifespan on
vests and caution against buying used vests unless you know

(03:47):
the manufactured date and the materials used to make it.
As with any product or idea or anything, really, we
recommend always doing your research, especially if your life might
be on the line. Today's episode is based on the
article how bulletproof are bulletproof vests? On how stuffworks dot com,

(04:09):
written by Jared w Alexander. Brain Stuff is production of
iHeartRadio in partnership with how stuffworks dot Com and is
produced by Tyler Klang. Four more podcasts my heart Radio,
visit the iHeartRadio app, Apple Podcasts, or wherever you listen
to your favorite shows.