Question

In a thermos flask cold liquid remains cold and hot liquid remains hoot .why?

Answer 1

All Hydro Flask bottles have double-walled, no-sweat insulation, which keeps hot liquidsfrom transferring heat and cold liquids from causing condensation on the outside of thebottle.

Answer 2

Back to The Thermos Bottle: The technical name of a thermos is a vacuum flask (you will know the reason why, shortly). To keep your drinks hot or cold, it minimizes heat transfer due to conduction and radiation. Convection is not included because convection keeps the temperature in a liquid even.