Steel Simple Modern insulated water bottles are made of high quality food grade 18/8 stainless steel metal. The bottle is highly rust resistant and it will.Vacuum Insulation Technology This bottle has a double-wall exterior with a vacuum seal between the walls. This means your drink temperature has no medium for the heat or cold to transfer through. Your drink will truly stay as hot or cold as long as possible.  Vacuum insulation provides superior heat retention--your beverage stays hot or cold for hours.Nonstick coated interior makes cleaning easy.Recommended Tip for Maximum Beverage EnjoymentIn order to maximize the incredible insulation technology, it is recommended to either pre-chill or pre-heat the bottle just prior to use. This can be accomplished by filling the bottle with hot water, attaching the lid and letting it rest for a few minutes. Before you are ready to use, simply empty the water and fill with your favorite beverage. Attaching the lid will further increase the thermal efficiency.