Hello, one-handed hydration. More hydration for more fun with our leakproof, Flex Straw Cap. Our 21 oz (621 ml) Standard Mouth with Flex Straw Cap is just the right size for staying hydrated before, during and after activity. Beverages stay cold for 24 hours and hot for up to 12. The Flex Straw Cap is leakproof and makes it easy to sip on the move. Learn more about Hydro Flask.