How does the thermos keep warm?

The three ways of heat transfer are: conduction, convection, and radiation.
To keep the water in the bottle warm, it is necessary to block the three ways of heat transfer from the water to the outside:
(1) The bottle liner of the thermos is double-glazed, the interlayer between the two layers is evacuated, and the cork is made of cork. This greatly reduces the heat transfer rate;
(2) The thermos is airtight. This blocks heat convection;

(3) There is a layer of reflective silver on the double glass of the thermos flask, which can reflect heat radiation. This greatly reduces the amount of heat radiated to the outside.