How is loss of heat minimized in a thermos flask ?

Explanation

A thermos flask is made up of a double walled glass bottle with evacuated space between the two walls .The inner surface of outer wall and the outer surface of inner wall are silvered .These polished surfaces reflect almost all the heat radiation falling on it However . if some heat radiations are transmitted by the inner polished wall , then these radiations are reflected by the inner surface of outer wall .Thus loss of heat is very small or minimised in flask due to double glass polished walls .Therefore , when a hot liquid is placed in thermos flask , it does not get cold for a long time . Similarly , when a cold liquid is placed in flask , it does not get hot for a long time .