The How Stuff Works 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...
Quite an interesting page on how body armor works. It discusses the differences between soft and hard body armor. One thing I found interesting was the discussion about the different types of ceramics used. Most body armor uses a ceramic material called alumina. It's the same stuff sapphires are made out of.
Most body armor use kevlar as a bullet proofing material but there is another material called vectran which is approx. 2 times stronger than kevlar that is also used. Also spider silk, and carbon nanotubes are capable of making bullet proof material.
This also stuck out as something of interest:
That's comforting.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.