The flasks 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.