The 500ml is part of our ultralight range and is so light you might forget you brought it with you. Weighing just over an ounce, it's optimal hydration no matter what kind of runner you are. The flexible material fits in most pockets, it shrinks as you drink to minimize water movement and it can be used with or without a hose. A new feature, the SpeedFill™ cap, makes refilling the aid station a breeze. Ultra-lightweight, extremely useful.