A bulletproof vest, also known as a ballistic vest, works by absorbing and dispersing the energy of a bullet or other projectile, thereby reducing its ability to penetrate the body and cause injury. Here’s how it works in detail:

1. Materials Used: Bulletproof vests are typically made from high-strength fibers such as Kevlar, Twaron, or ultra-high-molecular-weight polyethylene (UHMWPE). These materials are chosen for their ability to absorb and distribute the force of a bullet.
2. Layering: The vest is made up of multiple layers of these fibers. When a bullet strikes the vest, it impacts the first layer and begins to deform. As the bullet passes through each successive layer, its energy is gradually absorbed and spread out over a larger area. This reduces the likelihood of the bullet penetrating the vest.
3. Energy Absorption: The fibers in the vest work by “catching” the bullet. As the bullet encounters resistance, it begins to flatten, and its kinetic energy is transferred to the fibers. The layered structure of the vest helps to dissipate this energy across a wider area, which helps to prevent penetration.
4. Stopping the Bullet: The goal of the vest is to slow down the bullet to the point where it either stops completely or its velocity is significantly reduced, causing minimal injury if it does penetrate.
5. Trauma Reduction: Even if a bullet does not penetrate the vest, the wearer can still suffer blunt force trauma from the impact. To mitigate this, some vests are equipped with trauma plates, which are hard inserts made from materials like ceramic or steel. These plates provide additional protection by further dispersing the force of the impact.
6. Protection Levels: Bulletproof vests are rated by the National Institute of Justice (NIJ) according to the level of protection they provide. The ratings range from Level IIA (protection against lower-velocity handgun rounds) to Level IV (protection against high-velocity rifle rounds).

While bulletproof vests provide significant protection, they are not completely invulnerable. The level of protection varies depending on the type of vest and the type of ammunition used.