Hydrapak Soft Flask 250ml Whether it's running trails, paddling rivers, or hitting the slopes, keeping fuelled up and hydrated is just a bite away. The collapsible, lightweight Hydrapak SoftFlask 250 is easy to fill and even easier to consume, with a patented soft silicone bite valve, and super easy to squeeze container. It can be integrated into a variety of running packs, run vests, waist belts, even PFDs.