Since the 1970s, when the first bullet-resistant vest appeared on the law enforcement scene, there has been a constant evolution of fibers, materials and vest design. Ballistic engineers can choose from polyethylene to micro-filament fabrics to create hybrid vests that offer the best ballistic protection in a lightweight and comfortable design. Designers and engineers must keep in mind that different materials offer different performance against different ballistic threats. It is also important that protective vests be wearable. "Officers don't get killed because bullets penetrate their armor; they get killed because they don't wear it." The article features design, manufacturing and testing procedures used by American Body Armor, an Armor Holdings company based in Jacksonville, Florida. Ninety-five percent of the company's tactical vests and 80 percent of its soft body armor is customized.