Before purchasing, you need to decide primarily on what type of deployment you'll need the vest for and what level of threat you'll face during it. This leads to the choice of composition of protective layers.
Like an onion
For the vest to function properly, it must not show any damage and must be properly assembled. The outer shell should contain a ballistic insert made of fiber material such as Kevlar, Twaron, or Dyneema, with an anti-shock insert inserted into the shell towards the body. In more advanced vests, an additional protective panel may be inserted on the outer side before the ballistic insert.
The ballistic insert captures fired bullets, and its effectiveness lies in the strength of the fibers in tension. Most bullets deform and rotate upon impact, winding the fibers around themselves and tending to stretch them. The vest prevents this with the extreme strength of its fibers. However, the soft material, when impacted by the energy of the bullet, bends towards the body (with a 9mm projectile impact, up to 3 cm), which can cause internal injuries. Therefore, an anti-shock insert made of aramid or polycarbonate, or polyurethane materials, is incorporated into the vest. It reduces the deflection of the ballistic insert by up to 40% and spreads it over a larger area.
In real armor, an additional ballistic panel transforms the vest, which is inserted to increase protection against rifle bullets. It can push the protection level up to TBO 7 CZ (according to standard ČSN 39 5360), which means survival when hit by a 7.62×54 mm R round. Modern panels are made of ceramic-aramid composite and are embedded in a water-repellent fabric cover. They are inserted into pockets on the surface of the vest (referred to as plate carriers), so that the bullet deforms and flattens here before penetrating the Kevlar. This allows more fibers to engage in stopping the projectile.
However, additional plates are worthwhile only when there is a threat of the use of high-performance weapons on the opponent's side - they significantly increase weight and limit movement. The effort to balance protective capability (associated with high weight) and mobility (requiring low weight) has been a recurring theme throughout the history of ballistic vest development.
Watch out for size
In recent times, inserts against knives made of materials like titanium mesh are often implemented into vests. After all, ballistic vests were originally designed to protect against firearms, so even a robust model can be pierced by a knife or penetrated by a crossbow or more powerful bow. The reason is the different nature of penetration by an arrow/blade through the material - unlike projectiles, sharp objects do not tear the fibers but cut or deflect them to the sides.
It should be noted that some parts of vests, such as fastening straps, are still made of reinforced nylon even in the 21st century. Similarly, it is important to mention that the highest quality vests have fiber layers treated with a water-repellent finish - the resistance of materials when wet decreases because water acts as a „lubricant“.
Another criterion you should not overlook is the correct size. The vest must fit perfectly - and don't automatically count on the possibility of adjustment by tightening, as with the waist circumference of tactical pants. While the vest can usually be adjusted to body proportions in the shoulder area, it is usually only minimal. Underestimating thorough testing can have fatal consequences in action.
Choosing a small vest exposes the upper chest or abdomen above the belt. Alternatively, the vest may not be securely fastened on dry zippers; during action, it may come undone - and there are few things more useless than an exposed ballistic vest with its dangling parts hindering movement. A poorly fitted vest also exposes the hips under the shoulders, and thus most of the internal organs.
When using a model that is too large, the fighter becomes an unwieldy monster that endangers itself. A vest that is overly large may constrict the upper edge of the front part while sitting in a vehicle, while the lower edge prevents access to the belt - so „digging out“ a spare magazine or handcuffs is difficult.
Levels of protection
For easier orientation, vests are divided into several categories, or rather standards of ballistic resistance classes (TBO). The most commonly used classification is the American one according to the National Institute of Justice (NIJ), which distinguishes four basic classes. The lightest Type I vests stop bullets up to .22 LR and .380 ACP at speeds around 330 m/s, which NIJ practically does not consider bulletproof anymore. Type II can handle even .357 Magnum at 436 m/s, Type III stops rifle bullets like 7.62×51 mm (e.g., American M14) and 7.62×39 mm (Russian AK-47). Type IV includes vests that stop even special projectiles designed to penetrate vests, which travel at speeds up to 878 m/s. The younger and very strict Czech standard ČSN 39 5360 is also widely used.
However, regardless of the category the vest falls into, there is no one hundred percent reliable protection. An absolutely bulletproof vest is probably as much nonsense as an unsinkable ship, because effectiveness is influenced by many factors. For example, bullets of the same caliber, but different constructions - such as semi-jacketed ones - can be captured by the vest with different results. The deformability of the bullet and its external shape have a key impact. "Bees" with a steel core exhibit exceptionally high penetration, where minimal deformation occurs, so only a limited number of fibers can engage in slowing it down. Manufacturers guarantee resistance to such ammunition only when using an additional metal or ceramic panel.
