Withstanding Blunt Trauma
Besides stopping a bullet from reaching your body, a piece of body armor also has to protect against blunt trauma. Blunt trauma can be caused by the force of the bullet. Essentially, bulletproof vests have to spread the blunt trauma out over the whole vest. That way 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. This increases their density and their thickness at each point. To make it even more rigid, the material is coated with a type of resin. Then it's sandwiched between two layers of plastic film.

Layers of Kevlar® fiber slow the bullet down to prevent serious injury. The impact with the Kevlar® layers causes teh bullet to spread out at the tip. As it does so, it begins to resemble a mushroom.

KEVLARŪ is very tightly woven, so much so that it doesn't have a lot of 'give' to it - meaning it doesn't move much. Since no one layer or "net" of the KEVLARŪ can move a good distance, bullet proof vests are made of several layers of KEVLARŪ. Each layer (net) slows the bullet a little bit more, until the bullet finally stops. The material also causes the bullet to spread out at the tip. It's similar to when 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."

A person wearing body armor will still feel the energy of a bullet's impact but over the whole torso rather than in a specific area. When it works correctly, the vest will prevent serious injury. No bulletproof vest is completely impenetrable, however. Right now, there is no piece of body armor that will make a person invincible to attack.