Hydro Flask’s insulated water bottles are made of high quality 18/8 stainless steel and are double wall vacuum insulated. The bottles have no liner (like most aluminum bottles) and are BPA free. They are designed to be lightweight, making them great for long hikes, days at the beach, camping or long road trips. Unlike plastic water bottles or single wall stainless bottles, this will keep your beverage of choice at your preferred temperature for hours, whether you choose hot or cold.