Question

How does a vacuum flask work? Please don't just copy and paste from wikipedia

Answer 1

A vacuum flask does not (almost) allow heat transfer by any of the three ways that heat can travel. The silver coating on the inner bottle prevents heat transfer by radiation, and the vacuum between its double wall prevents heat moving by convection. The thinness of the glass (heat insulator) walls stops heat entering or leaving the flask by conduction. The case surrounding the flask provides additional insulation.

Note that heat transfer takes place even in vaccum flasks because nothing is perfect heat insulator and the material (liquid) in the vaccum flask radiates energy mainly in different wavelength bands (other than visible wavelength band). But the rate of this heat transfer is very small. That is why after a very long time even the liquid in the vaccum flask attains the room (surrounding) temperature.