Speaker 1: Welcome to brain Stuff, a production of iHeartRadio. Hey brain Stuff,
Speaker 1: Lauren vogelbomb here with a classic episode from our archives.
Speaker 1: Today's gets into the science and history behind bulletproof vests,
Speaker 1: how they work and when they don't work so well,
Speaker 1: Hey brain Stuff, Lauren Vogel bomb here. Bulletproof veests have
Speaker 1: saved plenty of lives, but this gear isn't perfectly well
Speaker 1: bulletproof in all situations.
Speaker 2: So exactly how well do they work? And do bulletproof
Speaker 2: vests degrade over time? Can they fail? Let's look at
Speaker 2: a bit of history. Early bulletproof vests were mainly made
Speaker 2: from polyperiphenline tarphalamide, better known as kevlar. It was invented
Speaker 2: by Stephanique Follack, a chemist working for DuPont in the
Speaker 2: early nineteen sixties. DuPont had already invented nylon and spandex,
Speaker 2: and was on the hunt for the next generation of
Speaker 2: high performance fibers. Synthetic fibers are created with polymers molecules
Speaker 2: composed of repeating subunits, effectively creating a linked chain of
Speaker 2: molecules that are more than the sum of their parts.
Speaker 2: What Kolk discovered would eventually become kevlar and would see
Speaker 2: application in tires, racing sales, and bulletproof vests. Bulletproof vests
Speaker 2: today are made from polyethylene fibers, a popular plastic polymer
Speaker 2: seen in nearly everything we use, grocery bags, toys, plastic
Speaker 2: trash bins, and so on. Polyethylene fibers, or pe as
Speaker 2: it's called, are woven in layers to form the guts
Speaker 2: of protective vests that are cheaper and stronger than kevlar.
Speaker 2: In nineteen eighty nine, a company called Allied Signal developed
Speaker 2: a competitor for kevlar and called it Spectra Shield. Originally
Speaker 2: used for sailcloth, this polyethylene fiber is now used to
Speaker 2: make lighter, yet stronger material for use in bulletproof vests
Speaker 2: alongside the traditional kevlar. According to a manufacturer of bulletproof vests,
Speaker 2: the layers inside a vest are designed to reduce the
Speaker 2: velocity of a round to a point below the speed
Speaker 2: of sound. At roughly this point, the fibers can have
Speaker 2: time to react to the bullet and exert their toughness,
Speaker 2: of their strength, and how much they'll bend before they break.
Speaker 2: The more layers, or the greater the density of the
Speaker 2: weaving of those layers, the greater the toughness of the fibers,
Speaker 2: and the more capable they are of stopping a bullet.
Speaker 2: Most pistols fire bullets at velocities that are just slightly
Speaker 2: above the speed of sound. A bullet from a nine millimeter,
Speaker 2: for example, travels at around nine hundred and eighty feet
Speaker 2: per second. That's about three hundred and eighty meters per second.
Speaker 2: The speed of sound is around one thousand, one hundred
Speaker 2: and twenty feet or three hundred and forty meters per second. Thus,
Speaker 2: a good vest doesn't need to work too hard to
Speaker 2: bring a nine millimeter bullets velocity down to a point
Speaker 2: where it can make use of the toughness of its fibers,
Speaker 2: and slugs from shotguns travel even slower, so they are
Speaker 2: relatively easy to stop as well. A rifle bullet, however,
Speaker 2: is another matter, entirely depending on the grain and quality
Speaker 2: of the propellant. A bullet fired from an AR fifteen
Speaker 2: travels roughly three thousand, three hundred feet per second. That's
Speaker 2: about one thousand meters per second, which is nearly three
Speaker 2: times the speed of sound. It'll take a far greater
Speaker 2: density of ballistic fiber to stop that bullet. Most vests
Speaker 2: designed to stop rifle bullets are backed up with high
Speaker 2: density insert plates made from ceramics and polyethylene that break
Speaker 2: up a bullet into pieces and capture it. Vests without
Speaker 2: those plates would likely fail to capture a rifle bullet.
Speaker 2: The material of the vests themselves is also prone to
Speaker 2: break down for various reasons. Kevlar, for instance, degrades when
Speaker 2: exposed to salt such as the salt and human sweat.
Speaker 2: The longer a person exerts themselves while in a bullet
Speaker 2: proof vest made of kevlar to the tune of years,
Speaker 2: the greater the likelihood of failure. Vests made from polyethylene
Speaker 2: will also break down over time when exposed to UV light.
Speaker 2: Manufacturers say that there's about a five year lifespan on
Speaker 2: vests and caution against buying used vests unless you know
Speaker 2: the manufactured date and the materials used to make it.
Speaker 2: As with any product or idea or anything, really, we
Speaker 2: recommend always doing your research, especially if your life might
Speaker 2: be on the line. Today's episode is based on the
Speaker 2: article how bulletproof are bulletproof vests? On how stuffworks dot com,
Speaker 2: written by Jared w Alexander. Brain Stuff is production of
Speaker 2: iHeartRadio in partnership with how stuffworks dot Com and is
Speaker 2: produced by Tyler Klang. Four more podcasts my heart Radio,
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