The inner tank is composed of two glass bottles inside and outside. The two are connected at the mouth of the bottle, and the gap between the two bottles is vacuumed to weaken the heat convection. The surface of the glass bottle is plated with a bright silver film to reflect the infrared heat radiation. When the temperature inside the bottle is high, the heat energy of the contents is not radiated outward; when the bottle is cold, the heat outside the bottle is not radiated into the bottle. The thermos effectively controls the three heat transfer paths of conduction, heat convection and radiation.
The weak point of the thermos insulation is the bottle mouth. There is heat conduction at the connection between the inside and outside of the bottle, and the bottle mouth usually blocks the heat loss by cork or plastic plug. Therefore, the larger the capacity of the thermos bottle and the smaller the bottle mouth, the higher the heat preservation performance. The long-term maintenance of the vacuum of the wall of the bottle wall is extremely important. If the interlayer gradually inflates or damages the sealed suction tail, destroying the vacuum state of the interlayer, the insulation bottle loses the insulation performance.
In addition to the glass material, the thermos bottle is made of stainless steel or non-toxic and odorless plastic. The metal bottle is strong and durable, and is not easily damaged, but the thermal conductivity is much larger than that of the glass. The single-layer or double-walled container made of plastic is filled with foam insulation, which is light and convenient, and is not easy to be broken, but its heat preservation performance is inferior to that of the vacuum bottle.