Generally, it is a food container made of double-layer plastic or stainless steel plus vacuum layer or heat insulation layer. The top is covered and sealed tightly. The vacuum layer or heat insulation layer can delay the heat dissipation of food inside, thus achieving the purpose of heat insulation. The insulated lunch box is developed from the thermos bottle, and the insulation principle is the same as that of the thermos bottle. There are three ways to spread heat: radiation, convection and transmission. The silver liner in the heat preservation barrel can reflect heat radiation, and the vacuum layer or heat insulation layer of the cup can block heat transfer.
Modern thermal insulation lunch box adopts high-tech vacuum technology to vacuum the interior of double-layer high-quality 304 stainless steel, which can effectively block the heat source and achieve the effect of thermal insulation. The design is more humanized. Usually, it is designed in three or four layers. Put the lunch box and soup box with high temperature under the insulation barrel, then cover the insulation board in the middle, and then put the food box on it, which will not only bring you the best insulation effect, but also keep your food and beverage warm longer and fresher.
The principle of a thermos cup is the same as that of a thermos bucket. You can refer to the method that the thermos cup cannot be opened:
When you pour hot water into a cup, the air and water inside expand, but after a while they become cold and contract, so there is a pressure difference between the inside and outside of the cup and it can't be unscrewed. The solution is to overcome this pressure difference.