A thermos is a bottle that includes a double container. As a result, the air between the two walls is sucked out during the process of construction, thereby creating a vacuum. Due to the same, the thermos is designed to keep hot things and thus not allow heat to escape. Apart from the heat, the thermos can also keep things cold without the need for a cooling device. The same vacuum that keeps things hot tends to enter the scene and manages to keep it cool. So when you combine these aspects, a thermal bottle stands to be effective and efficient.
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