The modern thermos was invented in 1892 by the British physicist Sir James Dewar. At the time, he was working on a liquefaction of gas. The gas was liquefied at low temperatures. First, a container that could isolate the gas from the outside temperature was designed. So he asked the glass technician Berg to blow a pair for him. In a layered glass container, the inner walls of the two layers are coated with mercury, and then the air between the two layers is removed to form a vacuum. This kind of vacuum bottle is also called "du bottle", so that the liquid contained in it can be kept constant for a certain period of time regardless of the temperature of the crucible or the heat. Since the thermos in the home is mainly used for hot water insulation, it is also called a thermos. The construction of the thermos is not complicated. In the middle is a double-layer glass bottle, which is vacuumed between the two layers, and is plated with silver or aluminum. The vacuum state can avoid heat convection. The glass itself is a poor conductor of heat. The silver-plated glass can radiate the inside of the container. The heat is reflected back. Conversely, if the bottle contains cold liquid, the bottle can prevent external heat from radiating into the bottle.