Write note on flask of two walls or on thermos.

Explanation

Two walls flask or thermos bottle is an arrangement which exchanges the miniumu heat betweeen surroundings and system inside it and it is cylindrical vessel of glass of two walls.
Coating of silver is plated on inner and outer walls of this vessel.
The radiations are reflecting back to system inside the bottel by inner walls.
The radiations coming from surrounding are reflected by outer walls of silver plating.
By making the gap between these walls as free space, conduction and convection can be decreased.
This flask or thermos bottle is closed air tight by insulator cork.
The substance inside this remains hot or cold for some time.