The invention relates to a roundbaler (10) having a bale chamber (12) in whicha roundbale (16) can be produced, and a wrapping device (14) with which a completelypressedround bale (16) can be wrapped with a first film (18) in the bale chamber(12), and afeed device (24) for introducing the first film (18) into the bale chamber(12). Theroundbaler also comprises a feed point (21) at which the first film (18) canbe fed tothe bale chamber (12), and an ultrasonic sensor (42, 44) which is arranged atthe balechamber (12). The ultrasonic sensor (42, 44) is arranged at the bale chamberin such away that with the ultrasonic sensor (42, 44) it is possible to determinewhether the film(18) is present on a surface of the round bale (16). The invention alsorelates to adetection method for detecting a first film (18) on a surface of a round bale(16).
