Thermos's new hydration bottles give you the flexibility to choose what matters most. The double-wall option provides insulation and a sweat-proof design. Nothing is more vital to staying healthy and fit than proper hydration. Thermos hydration bottles make it easy to stay hydrated throughout the day. They're made of BPA-free materials, reusable and built to last. Please make sure that the seal is properly placed on the lid to ensure that the units do not leak.