@immibis @smokku @morpheo ...it's actually not.
Insulation stops heat transfer in both directions. The same techniques that hold heat in in the winter will also keep heat from entering in the summer. However, you need to have some provision to remove heat energy (i.e. a heat pump) in order to maintain a lower-than-ambient temperature.
@TechConnectify
precisely what i was thinking. a thermos is a thermos is a thermos.