How does a Soft Body Armor works?

From the National Institute of Justice standards, level I thru Level IIIA belongs to the soft body armor and level III body armor thru level IV belongs to the hard body armor. We all know how the hard body armor can protect us from the bullets but how about the soft body armor? 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.

When a bullet or projectile strikes body armor, it is caught in a "web" of high performance fibers that are layered and stitched to exceed certain bullet resistant specifications. The engaged fibers absorb and disperse the impact energy that is transmitted to the vest from the bullet, causing the bullet to deform or "mushroom". Additional energy is absorbed by each successive layer of material in the vest, until such time as the bullet has been stopped. Because the fibers work together in both the individual layer and with other layers of material in the vest, a large area of the garment becomes involved in preventing the bullet from penetrating, as well as dissipating the forces which can cause non-penetrating injuries to internal organs.

Since soft body armor deforms backward upon impact, it also deforms backward into the wearer of the vest. The damage to tissue caused by this transfer of kinetic energy is called blunt trauma. Minimizing blunt trauma helps save lives, since it not only reduces internal injury, but prevents temporary incapacitation during the initial hit, allowing the wearer to respond immediately in a high-threat situation.

Hard body armor just like level III body armor typically incorporates an ultra-hard, ballistic ceramic top layer combined with a laminated blend of unidirectional-oriented fiber bundles which work together to stop bullets and fragments.