Introduction of Bulletproof vest

A ballistic vest or bullet-resistant vest, often called a bulletproof vest, is an item of personal armor that helps absorb the impact and reduce or stop penetration to the body from firearm-fired projectiles- and shrapnel from explosions, and is worn on the torso. Soft vests are made of many layers of woven or laminated fibers and can protect the wearer from small-caliber handgun and shotgunprojectiles, and small fragments from explosives such as hand grenades.
Overview
Ballistic vests use layers of very strong fibers to "catch" and deform a bullet, mushrooming it into a dish shape, and spreading its force over a larger portion of the vest fiber. The vest absorbs the energy from the deforming bullet, bringing it to a stop before it can completely penetrate the textile matrix. Some layers may be penetrated but as the bullet deforms, the energy is absorbed by a larger and larger fiber area.

While a vest can prevent bullet penetration, the vest and wearer still absorb the bullet's energy. Even without penetration, modern pistol bullets contain enough energy to cause blunt force trauma under the impact point. Vest specifications will typically include both penetration resistance requirements and limits on the amount of impact energy that is delivered to the body.
Vests designed for bullets offer little protection against blows from sharp implements, such as knives, arrows or ice picks, or from bullets manufactured of non-deformable materials, e.g., those containing a steel core instead of lead. This is because the impact force of these objects stays concentrated in a relatively small area, allowing them to puncture the fiber layers of most bullet-resistant fabrics.By contrast, stab vests provide better protection against sharp implements, but are generally less effective against bullets.
Recent years
Since the 1970s, several new fibers and construction methods for bulletproof fabric have been developed besides woven Kevlar, such as DSM'sDyneema, Honeywell's Gold Flex and Spectra, Teijin Twaron's Twaron, Pinnacle Armor's Dragon Skin, and Toyobo's Zylon. These newer materials are advertised as being lighter, thinner and more resistant than Kevlar, although they are much more expensive. The US military has developed body armor for the working dogs who aid GIs in battle.
Since 2004, U.S. Special Operations Command has been at work on a new full-body armor that will rely on rheology, or the technology behind the elasticity of liquids in skin care and automotive products. Named TALOS, this new technology may be used in the future.
Performance standards
Due to the various types of projectile, it is often inaccurate to refer to a particular product as "bulletproof" because this implies that it will protect against any and all threats. Instead, the term bullet resistant is generally preferred.
Body armor standards are regional. Around the world ammunition varies and as a result the armor testing must reflect the threats found locally. Law enforcement statistics show that many shootings where officers are injured or killed involve the officer's own weapon.As a result, each law enforcement agency or para-military organization will have their own standard for armor performance if only to ensure that their armor protects them from their own weapons. While many standards exist, a few standards are widely used as models. The US National Institute of Justice ballistic and stab documents are examples of broadly accepted standards. In addition to the NIJ, the UK Home Office Scientific Development Branch (HOSDB – formerly the Police Scientific Development Branch (PSDB)) standards are used by a number of other countries and organizations. These "model" standards are usually adapted by other counties by incorporation of the basic test methodologies with modification of the bullets that are required for test. NIJ Standard-0101.06 has specific performance standards for bullet resistant vests used by law enforcement. This rates vests on the following scale against penetration and also blunt trauma protection (deformation)