Our water bottles were developed to perform in every environment. Each Hydro Flask is cast from double wall vacuum insulated food grade 18/8 stainless steel, therefore they are BPA-Free and resistant to bacteria and odors. The double wall vacuum insulation technology allows Hydro Flasks to keep contents hot for 12 hours and cold for 24 hours. The narrow mouth bottle is our original mouth size. It is ideal for keeping your liquids chilled all day. Ice cubes from standard refrigerator ice dispensers fit perfectly through the narrow mouth.