The double-walled TempShield vacuum-insulated bottle is made of sturdy stainless steel, with a relatively positive strength-to-weight ratio. In addition, the material is free of phthalates and bisphenol A, which negatively affect flavors and tastes, as well as our health. The Hydro Flask 32 oz Wide Flex Cap (946 ml) Travel Bottle - Stone also has a wide, convenient opening that allows for easy cleaning of the interior and direct insertion of ice cubes into drinks.