Hatmana is forbidden on Shabbat and applies to an item or structure that retains heat.

• You may not, during Shabbat, place a food container in an item or structure, such as a blanket, that retaines heat. You may do so if the food container was already wrapped before Shabbat.
• You may not add insulation (which will help keep in the heat) even before (and certainly not during) Shabbat to foods that are on a heat source, even to fully cooked foods, whether the foods are wet or dry.
• You may not apply heat to an insulated utensil--or apply any insulation that adds heat--even before Shabbat began and let it remain that way during Shabbat--even if the food was completely cooked before sunset on Friday.

SITUATION You wrap a pot in blankets before Shabbat, serve the food on Shabbat, and return it to a non-heat source.
WHAT TO DO You may rewrap it after eating to retain heat for later.