A new polyurethane-based material could mean self-hardening, almost impenetrable helmets

The Army Research Laboratory has developed a polyurethane elastomer that withstands high-speed micro bullets, and could be used for helmets, face shields, and vests.

Even laser-launched micro bullets could not penetrate the new material developed by the Army Research Laboratory (ARL) during tests this month. Made out of polyurethane urea elastomers (PUUs), rather than the polyethylene materials typically used, the new material could be used for helmets, face shields, and vests to protect soldiers under fire.


The PUUs are formed through the linkage of the Polyurethane and Polyurea compounds. Both compounds contain negative isocyanate ions, according to a publication by Covestro, an industry specialist.


The resulting PUUs has hyper elastic properties, which means that it bounces back after impact so quickly that it is as though the material is hardening in response to impact, according to Dr. Alex Hsieh of the ARL. Where other materials puncture under levels of strain of around 108/s, PUUs are just compacted to about half their usual thickness, reports the ARL.


To develop the new elastomer material, the ARL collaborated with the Army’s Institute for Soldier Nanotechnology at MIT. Together, researchers from both have been conducting tests of the new material, pitting it against the laser-launched silica bullets mentioned above.


In order to conduct the tests, a pulsed laser was attached to the launching pad of the micrometer sized silica bullets, with a glass and gold platform separating the laser from the silica spheres themselves. According to the ARL press statement, previously tested elastomer materials have been penetrated by the micro-bullets or failed to bounce back. The PUUs, however were not penetrated, and demonstrated resiliency and “hardening” behavior, reported Hsieh.


“[PUUs] generally have…low resistance to elastic deformation under loading at ambient conditions, and higher failure strain–the capability to sustain significantly greater amount of strain before failure–than most of the plastic materials,” explained Hsieh.


The other key asset of PUUs is that the researchers have been able to alter the extent to which an impact compacts the material by rearranging the molecules of the PUUs. For example, the team was able to change the molecular composition of the PUUs so that it responded to impact by contracting only 50 percent of its original thickness, according to the ARL.


More development and testing remains to be done, and the ARL has not announced when the material will begin to be used. However, the researchers state that the new material will make the next generation of helmets, face-shields, and ballistic vests more resilient and less likely to puncture on impact.