Part-1: Labelled diagram of a thermo flask
Part-2: Explanation
Following are the factors which minimised the transfer of heat by conduction, convection and radiation in a thermo flask:
The vacuum between the two walls, rubber, glass, cork and air do not allow the loss of heat by conduction.
Cork in the neck of the flask and the cup over it prevent loss of heat by convection.
Heat cannot be lost by conduction or convection because of the vacuum between the two walls.
Heat loss is also minimised by radiation, by making the outer surface of the inner wall and inner surface of the outer wall silvered. The inner wall is a bad radiator and the outer wall is a good reflector of radiation.
Thus, the transfer of heat either from inside to outside or from outside to inside is very little and the contents of the bottle can remain at the same temperature for a long time.