A feeding unit for feeding a plastic film in packaging machines for wrapping paper rolls, including: a unit for unwinding the film from a reel; a cutting device adapted to cut the film transversely; a transfer device including, on the right and on the left side of the feeding unit, drive belts configured for engaging the upper and lower faces of the film; and a positioning device including, on the right and on the left side of the unit, a predetermined number of drive belts configured for engaging the upper and lower faces of the film. On each side of the feeding unit, the transfer device comprises two pairs of belts. On each side of the feeding unit, the positioning device comprises a third pair of belts. The three pairs of belts are actuated by independent actuators.