How do insulated food bags work? What's physics behind and is it called something else other than insulation?

How do insulated food bags work ? You know, the ones that keep your hot foods hot and your colds foods cold ? I know that it traps the heat but what's special about the material they use ? What kind of material is it anyways ?|||Best heat insulation is the vacuum.


Heat does not travel through vacuum


But it is very hard and expensive method (other than mass produced vacuum jugs).





Air is also an insulator, and easier to handle (like double glazing on the windows)





There are fabricated materials, whose heat transfer coefficient is low, and they are used in the industry widely. One of the best insulating material is STYROFORM or POLYURETHANE as they use inside the walls of the refrigerators.