Vacuum flask (Thermos)

A vacuum flask, commonly known as a Thermos, is a container designed to keep liquids hot or cold for extended periods. It achieves this by minimizing heat transfer through three main features: a double-walled structure, with an air or vacuum layer between the walls, reducing heat conduction and convection; reflective coatings that reflect thermal radiation; and secure stops to reduce heat loss from evaporation. These design elements work together to maintain the temperature of the contents, making it an effective tool for storing beverages or liquids at desired temperatures over time.