This 500 ml flask features a soft, high-flow bite valve so you don't lose a drop and a small cap; 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.