Abstract: A flexible heating foil including a flexible support layer on which at least one electrically conductive heating track is arranged between two electrodes. The two electrodes supply the heating track with current. The flexible support layer includes a woven synthetic sheet, on which the at least one heating track is arranged and has one or more slitted areas that serve as expansion joints. The flexible heating foil can be used, for example, as a seat heater in a motor vehicle or as a heating foil to be worn on the body, such as in articles of clothing.