Heating elements for respiratory tubing (73) comprise an electrically-insulating substrate (22, 45, 50) with a printed looped track (21, 31, 41) of carbon extending along the substrate between two metal terminals (25, 26, 43, 44, 74, 75) at one end. The heating elements are preferably made by printing several looped tracks (51 to 59) side by side on an insulative substrate (50), applying a metal bus bar (60) along one edge (61) of the sheet over the free ends of the track loops. The bus bar is cut between the free ends of the tracks (51 and 59) to form isolated terminal pads connected with opposite ends of the tracks. The sheet is cut (63) between the tracks (51 to 59) to divide it into separate heating elements.
