Special
thanks to Bullet
Proof ME for providing the photos used in this
article.
Humans
have been wearing armor for thousands of years. Ancient tribes
fastened animal hide and plant material around their bodies
when they went out on the hunt, and the warriors of ancient
Rome and medieval Europe covered their torsos in metal plates
before going into battle. By the 1400s, armor in the Western
world had become highly sophisticated. With the right armor,
you were nearly invincible.
Photo courtesy Bullet
Proof ME A Pro MAX
bulletproof vest, designed for easy concealment under
normal
clothing
All that changed with the development of cannons and
guns in the 1500s. These weapons hurl projectiles at a
high rate of speed, giving them enough energy to penetrate
thin layers of metal. You can increase the thickness of
traditional armor materials, but they soon become too
cumbersome and heavy for a person to wear. It wasn't until the
1960s that engineers developed a reliable bullet-resistant
armor that a person could wear comfortably. Unlike traditional
armor, this soft body armor is not made out of pieces
of metal; it is formed from advanced woven fibers that can be
sewn into vests and other soft clothing.
In this edition of HowStuffWorks,
we'll look at soft body armor and other modern armor
technologies to see how they can stop bullets. We'll also find
out about the range of body armor options available and see
how the government tests and rates body armor.
Stopping Bullets Modern body armor is
divided into two main categories: hard body armor and
soft body armor.
Hard body armor, made out of thick ceramic or metal
plates, functions basically the same way as the iron suits
worn by medieval knights: It is hard enough that a bullet or
other weapon is deflected. That is, the armor material pushes
out on the bullet with the same force (or nearly the same
force) with which the bullet pushes in, so the armor is not
penetrated.
Photo courtesy Bullet
Proof ME Bulletproof
helmets for police use (left) and military use
(right)
Typically, hard body armor offers more protection than soft
body armor, but it is much more cumbersome. Police officers
and military personnel may wear this sort of protection when
there is high risk of attack, but for everyday use they
generally wear soft body armor, flexible protection that you
wear like an ordinary shirt or jacket.
Soft body armor is a fairly mystifying concept: How
can a soft piece of clothing stop bullets? The principle at
work is actually quite simple. At its heart, a piece of
bullet-proof material is just a very strong net.
To see how this works, think of a soccer goal. The back of
the goal consists of a net formed by many long lengths of
tether, interlaced with each other and fastened to the goal
frame. When you kick the soccer ball into the goal, the ball
has a certain amount of energy, in the form of forward
inertia. When the ball hits the net, it pushes back on the
tether lines at that particular point. Each tether extends
from one side of the frame to the other, dispersing the
energy from the point of impact over a wide area.
The energy is further dispersed because the tethers are
interlaced. When the ball pushes on a horizontal length
of tether, that tether pulls on every interlaced vertical
tether. These tethers in turn pull on all the connected
horizontal tethers. In this way, the whole net works to absorb
the ball's inertial energy, no matter where the ball hits.
In a bulletproof vest, several layers of
bullet-resistant webbing (such as KEVLAR) are sandwiched
between layers of plastic film. These layers are then
woven to the carrier, an outer layer of traditional
clothing
material.
If you were to put a piece of bulletproof material under a
powerful microscope,
you would see a similar structure. Long strands of fiber are
interlaced to form a dense net. A bullet is traveling much
faster than a soccer ball, of course, so the net needs to be
made from stronger material. The most famous material used in
body armor is DuPont's
KEVLAR fiber. KEVLAR is lightweight, like a traditional
clothing fiber, but it is five times stronger than a piece of
steel of the same weight. When interwoven into a dense net,
this material can absorb a great amount of energy.
In addition to stopping the bullet from reaching your body,
a piece of body armor also has to protect against blunt
trauma caused by the force of the bullet. In the next
section, we'll see how soft body armor deals with this energy
so that the wearer doesn't suffer severe injuries.
Let Me Be Blunt In the last section, we saw
that a piece of soft bulletproof material works in the same
basic way as the net in a soccer goal. Like a soccer goal, it
has to "give" a certain amount to absorb the energy of a
projectile.
When you kick a ball into a soccer goal, the net is pushed
back pretty far, slowing the ball down gradually. This is a
very efficient design for a goal because it keeps the ball
from bouncing out into the field. But bulletproof material
can't give this much because the vest would push too far into
the wearer's body at the point of impact. Focusing the
blunt trauma of the impact in a small area can cause
severe internal injuries.
Bulletproof vests have to spread the blunt trauma out over
the whole vest so that the force isn't felt too intensely in
any one spot. To do this, the bulletproof material must have a
very tight weave. Typically, the individual fibers are
twisted, increasing their density and their thickness
at each point. To make it even more rigid, the material is
coated with a resin substance and sandwiched between
two layers of plastic film.
A person wearing body armor will still feel the energy of a
bullet's impact, of course, but over the whole torso rather
than in a specific area. If everything works correctly, the
victim won't be seriously hurt.
Since no one layer can move a good distance, the vest has
to slow the bullet down using many different layers. Each
"net" slows the bullet a little bit more, until the bullet
finally stops. The material also causes the bullet to
deform at the point of the impact. Essentially, the
bullet spreads out at the tip, in the same way a piece of clay
spreads out if you throw it against a wall. This process,
which further reduces the energy of the bullet, is called
"mushrooming."
No bulletproof vest is completely impenetrable, and there
is no piece of body armor that will make you invulnerable to
attack. There's actually a wide range of body armor available
today, and the types vary considerably in effectiveness. In
the next section, we'll see how this body armor is ranked, and
we'll look at how police officers and others decide which
level of protection to wear.
Ranking Resistance In the last couple of
sections, we saw that modern soft body armor consists of
several layers of super-strong webbing. This material
disperses the energy of a bullet over a wide area, preventing
penetration and dissipating blunt trauma. This sort of armor,
as well as hard armor, ranges considerably in effectiveness,
depending on the materials used as well as the armor design.
In the United States, body armor is tested and rated by the
Office
of Law Enforcement Standards (OLES). Based on extensive
laboratory tests, researchers classify any new body-armor
design into one of seven categories: Category I body armor
offers the lowest level of protection, and category VII offers
the highest. The body-armor classes are often described by
what sort of weaponry they guard against. The lowest-level
body armor can only be relied on to protect against bullets
with a relatively small caliber (diameter), which tend
to have less force on impact. Some higher-grade body armor can
protect against powerful shotgun fire. Categories I through
III mostly designate soft body armor, while higher-ranked
suits typically include hard-armor elements.
Photo courtesy Bullet
Proof ME The front (left)
and back (right) of a hard-armor steel plate. The plate
has been shot with several different rifle rounds, all
of which were deflected. The highest caliber round
created a slight dent in the back of the plate, but none
of the shots would have caused significant blunt
trauma.
Generally speaking, armor with more layers of bulletproof
material offers greater protection. With some bulletproof
vests, you can add layers. One common design is to fashion
pockets on the inside or outside of the vest. When you
need extra protection, you insert metal or ceramic plates into
the pockets. When you don't need as much protection, you can
wear the vest as ordinary soft armor.
To determine how effective a particular armor design is,
the OLES researchers shoot it with all sorts of bullets, at
all sorts of angles and distances. For a piece of armor to be
considered effective against a particular weapon at a
particular range, it has to stop the bullet without causing
dangerous blunt trauma. The researchers determine blunt trauma
by molding a layer of clay onto the inside of the armor. If
the clay is deformed more than a certain amount at the point
of impact, the armor is considered ineffective against that
weaponry.
It may seem odd that a police officer would wear category I
body armor, which will only stop relatively small-caliber
bullets, when they could have superior protection from
higher-ranked armor. But there is a very good reason for this
decision. Typically, higher-ranked armor is a lot bulkier and
heavier than lower-ranked armor, which results in several
problems:
Photo courtesy Bullet
Proof ME Bulletproof
waistcoat designed for everyday civilian
wear
An officer has reduced flexibility and comfort in
bulkier armor, which impedes police work. You can't chase a
criminal very well when you're carrying a massive weight on
your torso.
Heavier armor may actually increase the chances of an
officer being severely wounded. An attacker would be more
aware of a heavy armored jacket than a thin concealed vest,
and therefore might aim at an unarmored part of the body,
such as the head.
The discomfort of heavier armor makes it more likely
that an officer won't wear any protection at all. Police
departments are very careful to select bulletproof vests
that are relatively comfortable in order to encourage
officers to actually put them on.
Armor effectiveness and comfort are sure to improve in the
future as technology companies develop lighter, stronger
materials. We are certainly a long way from impenetrable
armor; but in 50 years, advanced armor will give police
officers a much greater level of protection when they're
walking the beat. Most likely, we will also see an increase in
civilian body armor in the years ahead. There is an
ever-growing market for comfortable soft body armor that can
fit under clothes, or even be worn as an outer jacket. With
gun violence on the rise, many citizens feel as if they're
walking onto a battlefield every day, and they want to dress
accordingly.
To learn more about civilian body armor, and the many other
sorts of body armor on the market, check out the links on the
next page.
