The principle of cooking with retained heat has been known for its usefulness in many times and many cultures. Peasants wrapped pots of partially cooked food in heavy feather beds. Well insulated, the food would continue to cook until the family returned from the fields to a hot meal. Native Americans used heated stones for clam bakes. Members of logging camps baked beans over hot stones in pits. Farmers carried fireless cookers into the fields so they could enjoy a hot meal at noon. Immigrants to America used their iceboxes as fireless cookers during the winter. Campers have used their sleeping bags to cook with retained heat.