What Our Gearhead(R) Experts Are Saying:"The Hydraulics 500ml Soft Flask is my go-to for runs and fast hikes. It fits perfectly in a vest pocket, doesn't slosh, and the bite valve delivers a steady flow without leaks. I also love how easy it is to fill with ice or mix electrolytes thanks to the wide opening."When we're moving light and fast, the Hydraulics 500ml Soft Flask keeps hydration close and convenient. Built to slip seamlessly into running vests or pack pockets, this collapsible flask features a wide 42mm opening for easy filling with water, ice, or drink mix-so we can fuel up without breaking stride. A high-flow, self-sealing bite valve makes sipping effortless, while the TPU and RF-welded seams keep things durable, flexible, and leak-free. The tapered shape slides smoothly into vest pockets, and the easy-grip twist cap simplifies refills on the go. Pair it with the UltraFlask Filter Cap (sold separately) for clean water access on any trail. Lightweight, packable, and built for endurance-this soft flask is the perfect companion for every mile.