Thermally insulating food holders such as crock pots have been used in microwave ovens to keep food once cooked warm and to provide for simmering. However, such dishes do not thermally insulate foods well due to radiation of thermal energy from the food body both into and through the walls of the crock pot. This results in having to supply excess microwave energy to the crock pot. Also, the energy used for heating the crock pot may be regarded as wasted energy since it does not contribute to actually cooking the food.