The invention relates to a roundbaler (10) having a balechamber (12) in which a round bale (16) can be produced, anda wrapping device (14) with which a completely pressed roundbale (16) can be wrapped with a first plastic film (18) in thebale chamber (12), and a feed device (24) for feeding the firstplastic film (18) into the bale chamber (12). The roundbaleralso comprises a feed point (21) at which the first plasticfilm (18) can be fed to the bale chamber (12), and anultrasonic sensor (42, 44) which is arranged at the balechamber (12). The ultrasonic sensor (42, 44) is arranged atthe bale chamber in such a way that with the ultrasonic sensor(42, 44) it is possible to determine whether the first plasticfilm (18) is present on a surface of the round bale (16). Theinvention also relates to a detection method for detecting afirst plastic film (18) on a surface of a round bale (16).
