Bulletproof

Bulletproof is a common but imprecise term for materials and devices intended to resist penetration by firearms. In technical contexts, 'bullet-resistant' is preferred because no material is completely impervious under all conditions. Protection levels vary with threat type, impact angle, and the construction of the item.

Common implementations include body armor, vehicle armor, and ballistic glass. Modern body armor uses layers of high-strength fibers such as aramids (Kevlar, Twaron) or ultra-high-molecular-weight polyethylene, sometimes reinforced with ceramics or steel plates. Soft armor provides flexibility for the torso, while hard armor uses plates to stop higher-energy rifle rounds.

Standards and testing: In the United States, the National Institute of Justice (NIJ) defines ballistic resistance levels: IIA, II, IIIA for soft armor and III, IV for hard armor. Level III can protect against many intermediate rifle rounds; Level IV is designed to stop armor-piercing rifle rounds. Other countries use VPAM, STANAG, and other test methods.

Limitations: Even high-level armor has vulnerabilities: limited coverage areas, potential for spall, blunt force trauma, and defeat by certain ammunition types or rifle rounds at long range or through angle. Armor durability degrades over time and with environmental exposure; performance depends on fit and maintenance.

History: The phrase arose from early armor concepts; modern bullet-resistant materials emerged in the mid-20th century, notably with Kevlar, developed by Stephanie Kwolek at DuPont in 1965, leading to widespread soft armor in the 1970s. Ballistic glass and vehicle armor have since become common in both civilian and defense contexts.