A vacuum tumbler, also known as a vacuum insulated flask or a thermal flask, is a container designed to maintain the temperature of its contents—hot or cold—for extended periods. It achieves this by creating a vacuum between two layers of stainless steel or other heat-resistant materials. This vacuum acts as a poor conductor of heat, minimizing heat transfer in or out of the flask. When the tumbler is sealed, the air inside is mostly evacuated, leaving a thin layer of air or sometimes a gas like argon to prevent the metal walls from coming into direct contact with each other and conducting heat. This insulation is what allows the vacuum tumbler to keep contents hot for up to 12 hours or cold for up to 24 hours, depending on the model and the initial temperature of the contents. Vacuum tumblers are commonly used for beverages such as coffee, tea, or water, and are also suitable for soups, smoothies, and other liquids. They are popular among campers, hikers, bikers, office workers, and anyone who needs to keep their drinks or food at a desired temperature while on the go.