Why does the hot tea in the thermos flask remain hot for a long time?

Thursday, Jul,14th 2022

Traditional thermos flasks are Dewer flasks, they have an inner container surrounded by a vacuum, then the outer container.

Heat is conducted by 3 ways: conduction, convection and radiation. The vacuum limits conduction to the point where the inner container is attached to the outer container.

Convection is stopped by the lid or cap. Radiation is limited by the reflective inner container.

See picture below.