a dual wall cooking vessel is formed by the impact or friction bonding of the an inner to an outer vessel wherein a laminate of aluminum and copper layers is disposed between the outer surface of the bottom of the inner vessel and the inner surface of the bottom of the outer vessel . the aluminum layers are arranged to surround the copper layer of the uppermost aluminum layer being the upper aluminum layer being thinner than the lower aluminum layer and having a slightly smaller diameter than the copper and aluminum layer . the appropriate dimensions of the aluminum layers and sequence of welding and bonding operation results in the co - extrusion of both aluminum layers into a portion of the adjacent sidewall formed by the gap between the walls of the inner and outer vessel . this co - extruded layer s of aluminum within the side walls and the bottom of the vessel improves the heat transfer from the outer vessel to the inner vessel during cooking , but without significantly diminishing the insulating properties of the dual wall vessel that serve to keep the food warm while it is being served .