The Naked Running Flask feature a soft, high-flow bite valve so you don't lose a drop and a wide mouth cap for easy access and cleaning; and each bite valve has a dust cover for even better hygiene. And now Made of tough thermoplastic polyurethane (tpu), the flasks are bpa, phthalate and pvc free, and made from recyclable materials. They also feature a printed volume scale (in ml and oz) so you can monitor your fuel mix and consumption rate. Most importantly, they shrink in size as you use them to save space.
For best results, hand wash the flask and cap with mild detergent in warm water prior to using for the first and do the same thing before each use. Do not wash in dishwasher. Before using, make sure to not cross thread cap while screwing on or over tighten cap. It's a good idea to occasionally lubricate the cap and flask threads with with small amount of food grade cooking oil; be sure to wipe excess. When not in use keep cap loosely tightened on flask. If over time you notice your flask "yellowing" this is normal due to the materials used to make the flask flexible. Because this material is somewhat porous it can absorb elements that may be in tap drinking water and sports drinks' ingredients. This is normal and is certainly not unhealthy or dangerous. We recommend using Bottle Bright and following their instructions to renew and restore.