Eli5: Why can a thermal flask keep items cold for 24 hours, but only hot for 12 hours.

Question

Eli5: Why can a thermal flask keep items cold for 24 hours, but only hot for 12 hours.

In: Physics

Answer 1

Hot objects with high thermal energy emit light. This is called radiation. The steel on the outside of a Yeti thermos catches this radiation and keeps it away from the cold stuff inside.
If the stuff on the inside is hot, however, IT is what emits light. It heats up the inner layer of the thermos, and that layer radiates heat away.

The way they’re designed, it’s much easier to keep heat out rather than in.