Go big. The largest of our ultra-light series, the UltraFlask Speed 600 ml holds more so you can go the distance. Its soft material allows it to fit snugly in most vest pockets and it shrinks as you drink to minimize water movement. Topped with our newest SpeedFill(TM) cap feature that makes aid station refills a breeze. COMFORTABLE FIT Soft material conforms to most hydration vests, belts, or pack pockets COMPRESSIBLE Flexible design shrinks as you drink reducing water movement CUSTOMIZABLE HYDRATION Choose between a bite valve and a drink tube cap SPEEDFILL CAP Topped with a flip top cap for fast refills at aid stations