Abstract: A sheath device for heating breathing bags and hoses of underwater breath apparatus employs a fabric enclosure for the breathing bags, walls of which enclosure are formed of two layers sealed together at a plurality of discrete points to define water passages within sealed boundary lines. Tubular water conducting enclosures for the breathing hoses are connected to the enclosures in communication with the water passages in the walls, and flexible tubular dams connected to the device and to the hoses direct water flow from the wall passages into the hose enclosures.