In a method for manufacturing a winding tape (10) of unsintered polytetrafluoroethylene wherein polytetrafluoroethylene powder is mixed with a lubricating or slip agent, the material is molded into a cylindrical blank (1) and the blank (1) is first extruded as a strand with small outer dimensions and subsequently calendered into the tape (10) in the forming gap (13) of a pair of rolls (8,9). The surface of at least one roll is deformed under compression during calendering of the round rope (6) into the tape.