Aluminum foil usually helps maintain a food's temperature - whether high or low - because it retards the transfer of heat from the food to its surroundings and vice versa. Thus, a food protected by foil will retain heat and not freeze as quickly as it would in, say, plastic film.
Although aluminum foil is not the best choice for freezing, you can profit in other ways from its properties. Example, a food or section of a food can be wrapped with foil for slow thawing. If serving must be delayed, you can keep a hot food warm longer, or a cold food cool, in aluminum foil. Because a shiny surface reflects radiant heat, you can preserve heat by facing the shiny surface of the foil inward toward the hot food. By the same token, when keeping a food cold - perhaps for a picnic lunch - face the shiny side outward so it can reflect radiant heat away from the food.
** Asian Recipes