Liquids are great at absorbing bullets’ energy. Fired underwater, an AK-47 can only send a bullet a few feet forwards, while in the air the same bullets would easily fly over 1,000 feet. This is great news for secret agents looking to avoid henchmen by swimming underwater, but it’s impractical advice for anyone else unless they want to carry six-foot-thick tanks of water around themselves at all times. Fortunately, researchers have found liquids that work even better than water at stopping bullets. The latest, developed by Poland’s Military Institute of Armament Technology in Warsaw, is a new non-Newtonian Shear Thickening Fluid, and it might replace Kevlar in body armor of the future.
Shear-thickening fluids, unlike other liquids, harden when struck by a strong impact. (For examples in a bullet-free setting, watch people walk across a vat of corn starch and water or pound their shielded fingers with a hammer.) With shear-thickening fluids (affectionately known as oobleck), the bullet’s force is absorbed by the liquid, then dissipated outwards through the fluid medium.
Poland’s liquid armor isn’t the first. In 2010, British arms giant BAE announced a body armor made with Kevlar and shear-thickening fluid. Also in 2010, the U.S. Army Research Lab worked with scientists at the University of Delaware to develop a liquid body armor on the same principles, following research it started at the beginning of this century. In 2014, Iran boasted of making an armor built with shear-thickening fluids as well. In every case, the armor promises to absorb impacts better than kevlar, while reducing how far the armor itself is pushed into the wearer’s body.
With some many countries developing liquid armor, why haven’t we seen any in use? One reason is weight. In BAE’s tests, they found that the shear thickening fluid worked best when strengthened with Kevlar. The problem is that even thin layers of the fluid-Kevlar combination are heavier than multiple layers of Kevlar alone. If Poland’s formula, which the country is so far keeping secret, manages to be as strong without adding in Kevlar or taking on weight, it might clear the way for liquid armor that moves beyond concepts and into actual use.