The bottle has an inner wall and an outer wall, a vacuum between the two walls. Heat conduction and convection cannot be carried out in a vacuum, whereas the metallic reflective layer on the plating can reflect thermal radiation. So the liquid in the bottle can be poured in a fairly long period of time, maintain its original temperature. That is the reason why the thermos is warm and the drinks are cold in winter. Many people who have participated in many trips find it hard to imagine, without a thermos flask, a situation.
The Dewar produced liquid oxygen at the low temperature of 240, in order to preserve the liquid oxygen, he designed a heat can not be passed in, can not disperse the bottle. We use the Thermos flask, which is evolved from this "Dewar bottle". Dewar, the Thermos flask is based on the heat transfer design: ① It is made of two layers of glass bottles, and the vacuum is pumped in the middle. Isolate the heat conduction and convection of the air; ② the bottle walls coated with silver, as reflected in the mirror light, the heat can be reflected back into the bottle; ③ bottle lid, prevent the heat from the bottle to slip out, if used to install boiling water, it becomes a thermos flask.