A vacuum flask, also known as a thermos, is a container designed to keep liquids hot or cold for extended periods. It consists of two walls with a vacuum between them, which minimizes heat transfer. This design helps maintain the temperature of beverages, making it popular for carrying coffee, tea, or soup. Typically made from glass or stainless steel, a vacuum flask is lightweight and portable. Many models come with a screw-on lid that doubles as a cup, making it convenient for on-the-go use. They are widely used for outdoor activities, travel, and daily commutes.