A Thermos Flask for the Duke of Edinburgh

A Thermos flask of hot chocolate was the most wonderful thing I saw on the Duke of Edinburgh Silver expedition. Respect! The inside looks silver. It is made of a double layer of glass. The air has been expelled from between the layers so it is a vacuum. No particles so no transfer of energy by conduction or convection. But the flask will still get warm and emit infrared radiation. Silver surfaces are poor emitters of infrared - hence the glass is painted silver. The whole thing is encased in thick plastic to try to stop the glass fracturing.