A thermal flask, also known as a vacuum flask or thermos, is a container designed to keep liquids hot or cold for extended periods. It typically consists of two walls with a vacuum in between, which minimizes heat transfer. This design helps maintain the temperature of beverages, making it ideal for coffee, tea, or cold drinks. Thermal flasks come in various sizes and materials, including stainless steel and glass. They often feature a secure lid to prevent spills and may include additional features like built-in cups or handles for easy transport. Popular brands include Thermos and Contigo.