A heat exchanger cap, and method of manufacture of a heat exchanger cap configured to conform to a human head the cap comprising a first element for covering one side of the head； a second element for covering the other side of the head； and an intermediate joining element joined to, and which spaces apart, the first element and second element. Each of the elements define a single passageway for the passage of fluid through the cap. Each of the elements are provided with a flow interface in the region where the elements are joined. The flow interface defines an inlet for the passage of fluid into the passageway of one of the elements, and an outlet for the passage of fluid from the passageway out of the same element.
