How a Bullet-proof Vest Stops Bullets

Not all bullet-proof vests are actually bullet proof and some types are more effective than others. Those designed for use by soldiers are reinforced with hard armor plate, which also makes them heavier and able to withstand heavier-gauge fire. Most police departments and security forces have used soft vests for more than 20 years. These will not stop large-caliber ammunition, but are effective in most situations. Bullet-proof vests are usually filled with Kevlar -- a microscopic material made from polymer that looks like tightly woven gauze but has the strength of steel. Kevlar vests are light and generally very effective.

How Do Bullet-proof Vests Work?

• The effectiveness of bullet-proof vests is in the filling, not the outer covering. The soft vests worn by police consist of a tightly woven net of material, usually Kevlar, that distributes the force of the bullet and usually keeps it from penetrating through the back of the vest. By slowing the bullet's speed, the inner material absorbs much of the energy of the bullet, rendering it less damaging. When a bullet strikes the vest, its impact is distributed and the bullet is slowed and deformed. If the bullet does penetrate the vest, the force transmitted to the wearer is usually not great enough to do serious harm.

Military Vests

• Members of the military wear stronger, heavier vests.

  The body armor worn by the military consists of an outer shell of ceramic fabric called alumina. It is heavier and more cumbersome, but also more effective, than a soft vest. The outer shell resembles a suit of iron worn by knights in the middle ages and works in a similar fashion. The outer shell is hard enough to deflect a bullet so it cannot penetrate the inner material.

Injuries Still Occur

• A bullet hitting a soft vest is not harmless. The power and force of the strike against the body can still cause internal damage, pain and bruising. The impact of the bullet is spread over a larger area of the body but still with great force.

On the Horizon

• New fabrics are being developed that show great promise for use in bullet-proof vests. Vectran is said to be twice as strong as Kevlar and five to 10 times stronger than steel. Spider silk, a product of genetically engineered goats, produces a material called Biosteel, which is up to 20 times stronger than steel. Carbon nanotube thread is predicted to surpass Biosteel in strength but, currently, is prohibitively expensive.