Feeding unit for feeding a plastic film in packaging machines configured for the packaging of paper rolls, comprising: - a unit for unwinding the film from a corresponding reel; - a cutting device arranged downstream of the unwinding unit with respect to the direction followed by the film along an exit path from the unwinding unit and configured for transversely incising the film to allow to obtain sheets of predetermined length; - a transfer device arranged downstream of the cutting device and comprising, both on the right and on the left side of the feeding unit, a predetermined number of drive belts configured for engaging both the upper and lower faces of the film; and - a positioning device located downstream of the transfer device and comprising, both on the right and on the left side of the feeding unit, a predetermined number of drive belts suitable for engaging both the upper and lower faces of the film; characterized in that - both on the right and on the left side of the feeding unit, the transfer device comprises two pairs of belts (40, 41; 42, 43) arranged on opposite sides with respect to the path followed by the film, with a first pair of belts (40, 41) arranged immediately downstream of the cutting device and a second pair of belts (42, 43) arranged immediately downstream of the first pair of belts(40, 41); and - both on the right side and on the left side of the feeding unit, the positioning device comprises a third pair of belts (50, 51) arranged on opposite sides with respect to the path followed by the film, said belts (50, 51) being arranged immediately downstream of said second pair of belts (42, 43) of the transfer device; - both on the right side and on the left side of the feeding unit said three pairs of belts (40, 41; 42, 43; 50, 51) are driven by respective independent actuators; - the right side and the left side are defined by two flanks parallel to a direction of advancement of the film, and the distance between the said sides can be adjusted according to the film width. - a unit for unwinding the film from a corresponding reel; - a cutting device arranged downstream of the unwinding unit with respect to the direction followed by the film along an exit path from the unwinding unit and configured for transversely incising the film to allow to obtain sheets of predetermined length; - a transfer device arranged downstream of the cutting device and comprising, both on the right and on the left side of the feeding unit, a predetermined number of drive belts configured for engaging both the upper and lower faces of the film; and - a positioning device located downstream of the transfer device and comprising, both on the right and on the left side of the feeding unit, a predetermined number of drive belts suitable for engaging both the upper and lower faces of the film; - both on the right and on the left side of the feeding unit, the transfer device comprises two pairs of belts (40, 41; 42, 43) arranged on opposite sides with respect to the path followed by the film, with a first pair of belts (40, 41) arranged immediately downstream of the cutting device and a second pair of belts (42, 43) arranged immediately downstream of the first pair of belts(40, 41); and - both on the right side and on the left side of the feeding unit, the positioning device comprises a third pair of belts (50, 51) arranged on opposite sides with respect to the path followed by the film, said belts (50, 51) being arranged immediately downstream of said second pair of belts (42, 43) of the transfer device; - both on the right side and on the left side of the feeding unit said three pairs of belts (40, 41; 42, 43; 50, 51) are driven by respective independent actuators; - the right side and the left side are defined by two flanks parallel to a direction of advancement of the film, and the distance between the said sides can be adjusted according to the film width.