Designed in collaboration with soft flask leader Hydrapak, our DRINKFLASK500 500ml Soft Flask uses a thicker sleeve material for added puncture resistance. Bite-valve is easy to use and leak-free. Wide-mouth opening makes filling easy. Our DRINKFLASK500 Soft Flask is designed for use with water and Neversecond C30 Sports Drink and C90 High Carb drink mixes.