A pig for pipelines, in particular in the form of a cleaning or inspection pig, with a central unit and at least one, in the longitudinal direction of the central unit, front and one rear sealing unit. The pig also includes at least one sensor device comprising a plurality of sensor arms, which is provided in particular for the measurement of a geometry or condition of the pipeline. At least one of the sealing units and preferentially the central unit are produced from a plastic material at least in sections. At least one sensor arm, distant from the central unit, is connected to one of the sealing units.