Ever since the beginning of time, warfare has existed. And the need for humans to protect themselves is already a basic need. From level I to level III body armor, man has searched for new and improved ways to harm his fellow man in order to impose his will upon his enemies.
There are two types of body armor: Hard and Soft armor. Each type has their own strengths and weaknesses. Hard body armor is made of ballistic steel or ceramic or other similar, inflexible material. Soft body armor is made from Kevlar, Spectra, Twaron, or any other fabric-like ballistic material. Hard body armor is much stronger than soft body armor - only hard armor is capable of defeating rifle caliber ammunition and some types of armor-piercing ammunition. However, hard armor is heavier (although recent advances in material technology is drastically bringing the weight down), and it is only capable of covering vital areas of a person - the heart and lungs, usually. It's impossible to construct, at least with current technology, a full vest or suit of hard armor. Hard armor is used in conjunction with soft body armor to absorb shots. Soft body armor, on the other hand, is flexible, lighter, and easier to wear. However, it can only stop pistol caliber ammunition, and generally only from pistols. While it is possible to construct a soft vest capable of defeating high velocity pistol ammunition, the vests begin to become hot, thick, and heavy.
Soft body armor, while it cannot stop very high velocity ammunition, it can stop tremendous amounts of slower ammunition, such as .45ACP, .40S&W, 00 Buckshot, and other types of ammunition fired at less than 1500 feet per second.
Hard body armor like level III body armor is used in a tactical situation to give the wearer extra protection against both high speed pistol caliber ammunition, and rifle caliber ammunition. Hard body armor is generally a rectangular plate of material, either ballistic ceramic or ballistic steel. Each material has their strengths and weaknesses.