Why does aluminium foil keep food warm?

Why does aluminium foil keep food warm?

Aluminum foil does not make food warm. It can keep food warm longer by trapping the hotter air inside, which then serves as an insulator, and by preventing interchange of the hot air inside with cooler air. Aluminum foil itself conducts heat very well so it isn’t an insulator itself. Instead it is a barrier that limits the mixing of the hot air inside with the cooler air outside. If you wrap the food with cotton napkins first and then with foil it will stay warm longer simply because the napkin holds the foil farther from the food, creating more space for insulating air.