The thermos bottle used at home can keep the temperature of hot water well. What is its principle? The cooling of hot water is caused by thermal convection, heat conduction and thermal radiation. The thermos bottle liner is made to solve the above three problems. The bottle mouth is blocked with a cork to prevent the convection of cold and hot air; The gap between the double-layer bottles and bladders is vacuumized, which solves the heat conduction; Coating a thin layer of silver on the bottle liner makes it a mirror for reflecting light and heat, thus using the silver layer to block the heat radiation from coming back. In this way, the heat will not be lost, and it will play the role of heat preservation.