What does it mean that Barack Obama was wearing "bullet-resistant clothing"?

Answers to your questions about the news.
Jan. 20 2009 4:52 PM

Does the Kevlar Number Come in a French Cuff?

Obama was wearing "bullet-resistant clothing." What's that?

See all of Slate's inauguration coverage.

Illustration by Rober Neubecker. Click image to expand.

Barack Obama was sworn in as the 44th president on Tuesday under tight security. He rode to the Capitol in an armored Cadillac limo, spoke behind a protective glass shield, and wore "bullet-resistant clothing." Is that the same thing as a bulletproof vest?

Not quite. The vests familiar from cop shows and news footage of SWAT teams are manufactured to be maximally effective with no consideration for how they might look under a dress shirt. It's unclear what brand of body armor Obama sported at the inauguration, but several companies produce discreet, thinner vests that can be worn underneath clothing, inserted into an outer layer (like a coat) or woven into a shirt. Miguel Caballero, a Colombian company, makes bullet-resistant leather jackets, polo shirts, Windbreakers, and ruffled tuxedo shirts, which range from a few hundred dollars to $7,000 in price. There is a trade-off between efficacy and subtlety since, as a rule, it's more expensive to manufacture thin-but-reliable vests and shirts.

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No soft material can provide complete security against all types of bullets or multiple hits in the same place (which is why the term bulletproof is out of vogue), but the National Institute of Justice (the Department of Justice's research agency) has developed standards for determining to what extent a product is "resistant." Type IIA armor, for example, should protect against a 9 mm-caliber, full-metal-jacketed, round-nose bullet traveling at 373 meters per second. Type IIIA (the highest standard for a flexible, as opposed to a hard, material) protects against a 357 SIG flat-nose bullet fired at a velocity of 448 meters per second.

One of the more common fabrics used in bullet-resistant vests is Kevlar, a lightweight, synthetic fiber that's about five times stronger than a piece of steel of the same weight. Manufacturers use very dense strands of Kevlar—500 to 1,500 filaments per strand of yarn—and weave it into a netting. Then they cover the weave with a plastic film.

To test body armor, lab technicians coat the inside of the fabric with clay. Then they fire bullets at it. A proper bullet-resistant shirt or vest should not only stop the bullet (i.e., not tear) but also prevent a dent in the clay of more than 44 mm—a larger dent indicates a dangerously high energy transfer, which could result in fatal blunt-force trauma.

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Explainer thanks Tom Dragone of Point Blank Solutions.

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Juliet Lapidos is a former Slate associate editor.