HYDRATION VEST COMPATIBLE: Wider flask form and 3D welded bottom fits most pack and larger vest pockets for a snug and secure fit. Does not include Run Straw. COLLAPSIBLE FLASK: Soft material conforms to any pocket, and shrinks as you drink to reduce movement and pack away easily when empty. PERFECT FOR AID STATIONS: UltraFlasks are equipped with our SpeedFill Cap designed for quick and easy refilling at aid stations. A side tab pops open the cap in one motion and snaps shut with a click. FILTER COMPATIBLE: Compatible with 42mm threaded backcountry water filters including the HydraPak 42mm Filter Cap. BEYOND LIFETIME WARRANTY: If you experience any issue, we’ll repair or replace the item for free. Whatever it takes to keep your adventure going.