A wrapping unit to fold a wrap around a group of smoking articles; the wrapping unit comprises: a spindle, which is provided with a tubular cavity, which is designed to accommodate the group of smoking articles and has: an outer base wall, an inner base wall opposite the outer base wall, and a pair of side walls, which are interposed between the two base walls (34, 35); a wrapping conveyor, which supports the spindle and moves the spindle along a wrapping path; a first feeding device, which is designed to insert the group of smoking articles into the tubular cavity of the spindle; a second feeding device, which is designed to feed the wrap to the spindle laying the wrap on the outer base wall of the spindle; a first folding device, which is designed to fold the wrap in a "U"-shape around the spindle laying the wrap on both base walls (34, 35); and a second folding device, which folds, on each side, a longitudinal wing of the "U"-folded wrap against a corresponding side wall of the spindle; the wrapping unit is characterized in that: the outer base wall of the spindle is larger than the inner base wall of the spindle; the side walls of the spindle have respective inclined portions, which form a non-right angle with the base walls (34, 35) and give a trapezoidal shape to a cross section of the spindle; the second folding device folds, on each side, a longitudinal wing of the "U"-folded wrap against the inclined portion of a corresponding side wall of the spindle; and the spindle is provided with a plurality of sucking holes, which are arranged through the inclined portions of the side walls of the spindle and are designed to hold, through suction, the longitudinal wings of the "U"-folded wrap. a spindle, which is provided with a tubular cavity, which is designed to accommodate the group of smoking articles and has: an outer base wall, an inner base wall opposite the outer base wall, and a pair of side walls, which are interposed between the two base walls (34, 35); a wrapping conveyor, which supports the spindle and moves the spindle along a wrapping path; a first feeding device, which is designed to insert the group of smoking articles into the tubular cavity of the spindle; a second feeding device, which is designed to feed the wrap to the spindle laying the wrap on the outer base wall of the spindle; a first folding device, which is designed to fold the wrap in a "U"-shape around the spindle laying the wrap on both base walls (34, 35); and a second folding device, which folds, on each side, a longitudinal wing of the "U"-folded wrap against a corresponding side wall of the spindle; the wrapping unit is characterized in that: the outer base wall of the spindle is larger than the inner base wall of the spindle; the side walls of the spindle have respective inclined portions, which form a non-right angle with the base walls (34, 35) and give a trapezoidal shape to a cross section of the spindle; the second folding device folds, on each side, a longitudinal wing of the "U"-folded wrap against the inclined portion of a corresponding side wall of the spindle; and the spindle is provided with a plurality of sucking holes, which are arranged through the inclined portions of the side walls of the spindle and are designed to hold, through suction, the longitudinal wings of the "U"-folded wrap. the outer base wall of the spindle is larger than the inner base wall of the spindle; the side walls of the spindle have respective inclined portions, which form a non-right angle with the base walls (34, 35) and give a trapezoidal shape to a cross section of the spindle; the second folding device folds, on each side, a longitudinal wing of the "U"-folded wrap against the inclined portion of a corresponding side wall of the spindle; and the spindle is provided with a plurality of sucking holes, which are arranged through the inclined portions of the side walls of the spindle and are designed to hold, through suction, the longitudinal wings of the "U"-folded wrap.