ForceFlex technology incorporates patented multi-injection molding of the lens with a flexible Thermo Plastic Urethane (TPU) frame. Due to this construction it can achieve a military ballistic level impact resistance at over 1000 feet per second. The TPU material allows the frame to flex and fit individual faces from large to small https://www.arksafety.com/sites/default/files/135-FF137.eps.jpg