A vacuum flask,  known as a thermos, is an insulated container designed to keep liquids hot or cold for extended periods. It consists of a double-walled vessel, with the space between the walls evacuated to create a vacuum. This vacuum layer minimizes heat transfer by conduction and convection, while the reflective coating on the inner surfaces reduces heat transfer by radiation. Made of high quality stainless steel, are commonly used to store beverages like coffee, tea, or cold water.