"HydraPak® UltraFlask Speed 500ml: The UltraFlask Speed 500ml is a soft, compressible hydration flask built for runners and trail athletes who need fast refills and secure carry during long runs, trail outings, and race-day efforts. Its wider shape and 3D welded bottom keep the flask stable inside a vest pocket or hydration pack, so it stays put rather than shifting as you move. The soft TPU construction molds to your pocket, which means less bounce and distraction during sustained efforts. Whether you're refilling at a backcountry stream or grabbing water at an aid station, this unisex flask handles everything with equal ease.The SpeedFill cap flips open for quick refills and snaps closed for a leakproof seal, so you spend less time stopped at water sources. A high-flow bite valve auto-seals after each sip, eliminating drips between drinks. The flexible design compresses as the flask empties, reducing internal water movement and keeping your carry balanced throughout a run. A 42mm opening accepts ice and drink mixes without funneling, and the threading is compatible with 42mm backcountry water filters, including the HydraPak 42mm Filter Cap. RF welded seams and abrasion-resistant TPU construction hold up to repeated use and the friction of vest pockets. The flask is 100% BPA & PVC free with a working temperature range that extends from frozen to a maximum of 60°C / 140°F.Why Our Fit Experts Love It""I grabbed the UltraFlask Speed 500ml for a long trail run and appreciated how quickly I could flip the SpeedFill cap open at a stream crossing and get moving again. It sat flat in my vest pocket the entire time and never created an awkward bulge as it emptied."" - Sawyer, Road Runner Sports Fit Expert, Wilmette ILWho It's Best ForThe HydraPak® UltraFlask Speed 500ml is best for runners and outdoor athletes who carry hydration in a vest or pack during long runs, trail runs, or races where fast refills and secure fit are priorities. It suits anyone who wants a compressible, filter-compatible hydration flask that stays stable and drip-free across varied conditions. If you're sourcing water along the route or need reliable hydration access without fumbling, this flask delivers. VIP Family members can take the UltraFlask Speed 500ml for a 90-Day test drive with our Perfect Fit Guarantee."