HYDRO FLASKA(R) 21 ounce STANDARD MOUTH FLEX CAP :: Whether you're running, training at the gym, or just running around town, make staying well-hydrated super easy and convenient with the Hydro Flask 21 ounce Standard Mouth Flex Cap Water Bottle. The most popular of the Hydro Flask products, this versatile, medium-sized water bottle provides top notch insulation power, keeping cold liquids icy cold for up to 24 hours, and hot liquids steaming hot for up to 6 hours. Plus, you can feel safe and socially responsible when you purchase the Hydro Flask 21 ounce bottle because it is BPA-free, recyclable and backed by a lifetime warranty.