With the Naked 350ml and 500ml soft flasks,you get even more world class performance out of your hydration system. Designed to maximize the ergonomics, and compatible with Naked Running Bands, the low profile flask with a 28mm cap and high flow bite valve shrinks as you consume your liquids, reducing its mass and volume. Weighing a scant 28g, it is the perfect companion for ultralight Naked products.