She also notes the market has expanded significantly from the early 1990s where monolithic — single fiber type — vests were the norm. "In the ballistics arena, many times the two materials (aramid and HPPE) are combined because the performance of each adds to the other synergistically," explains Wagner. "The hybrids come out as a benefit because each material adds its own special component to the vest. They create a great catcher's mitt for energy absorption."Building the perfect sandwich
With the fibers now woven or laminated into a rolled fabric product, the manufacturing of a ballistic vest begins with research, development and the building of a sandwich. Manufacturers weigh the benefits of aramid — releases body heat and moisture to create a more comfortable vest — and the benefits of HPPE — higher tenacity and chemical resistance. Based upon these qualities and the goals for the product, it is determined if the vest will be produced from a single fiber or a combination of materials.
According to Wagner, manufacturers have found that combining materials allows for lighter weights, a greater range of threat protection, and improved comfort, flexibility and backface deformation performance.
In the research and development process, a sandwich is created — a precise layering of ballistic materials to meet the desired threat level. As an example, a sandwich may have 21 layers — seven Gold Flex, seven Spectra Shield and seven Kevlar. "But not only are the ingredients of the sandwich important, it is equally important at what order they go in," explains Olsen.
In the research process, testers manipulate the order and number of layers to achieve the desired effect. In the end, the 21 layers may break down into three Spectra Shield, two Gold Flex, seven Kevlar, four Spectra Shield and five Gold Flex. "The layers are put in the order that accomplishes those functions of stopping and dissipating in microseconds at impact," says Olsen.
But not all sandwiches are created equal. Each threat level requires a different composition and layering. Olson also notes that to reverse the sandwich front to back would create entirely different results, and may cause the vest to fail.Putting the vest to the test
As the composition of the sandwich is being developed, 15-inch by 15-inch sample sandwiches are shot. The shooting range is designed such that the bullet trap is at the back preceded by a clay box. The clay in this box is kept at a specific temperature and used to measure backface deformation. Guidelines allow for up to 44mm of backface deformation, although medical professionals say the body can withstand 70mm to 80mm.
In front of the clay box, on which the sandwich is mounted, are the chronograph's three — start, stop and proof screens — that measure the bullet's velocity. "The difference between Levels IIA, II and IIIA is in bullet speed," explains Olsen. "The faster the bullet, the higher the threat level."
At the front of U.S. Armor's range is the mounting tower which holds a Thompson Contender. U.S. Armor uses this single-shot handgun because it has interchangeable barrels and can test for a variety of bullets and calibers.
Once the sample achieves the appropriate response — less than 44mm of backface deformation and resistance to rounds with an appropriate speed for the threat level in question — a vest-patterned sandwich is cut. "The panel will perform better than the 15-by-15 sample because there is more area to disperse the energy, but we want to put it in its worst-case situation first," Olsen explains.
Because the smaller sample already meets National Institute of Justice (NIJ) requirements, when making the full-size vest, it is inherently overbuilt with a greater margin of safety. "If you're building a product that peoples' lives are depending on, would you build it just to the very edge of performance? No," says Olsen. "By making it more difficult on ourselves when we create the product, we end up with a product that has the overbuild already in it."
Once the sandwich achieves NIJ-level testing, manufacturers then perform a V50 test. In this test, the same piece of armor is shot by increasingly faster bullets until a round penetrates the vest. Throwing out the fastest and slowest speeds, the remaining speeds are averaged to determine the V50 rating. "The V50 will show if a vest is degrading and at what rate," explains Olsen. "You never want it to go below the speed of the NIJ requirement bullet."