More hydration for more fun with the Hydro Flask leakproof, Flex Straw Cap. This 24 oz Standard Mouth bottle 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 when closed and makes it easy to sip on the move.