What Our Gearhead(R) Experts Are Saying: "I always keep a couple of these in my vest for races or long trail runs. They're light, collapse as you drink, and the 500ml size is perfect for aid stations or fast fill-ups on the go. Fits seamlessly in my running vest pockets."When staying light and moving fast is the goal, the 500ml Soft Flask makes hydration effortless. Designed to work seamlessly with running vests, handhelds, or as a backup bottle in your pack, this soft-sided flask holds just enough water for those high-output stretches between fill-ups. As you drink, the flask compresses to minimize bounce and bulk, making it a favorite for race day and long-distance training. The flexible TPU construction is durable enough for everyday trail use yet light enough to disappear when empty. Whether you're stocking aid station drop bags or upgrading your vest setup, this flask is built to move as efficiently as you do.