An apparatus, and a related method, for unwinding reels and for joining a ply between two reels including a first unwinder adapted to unwind a first reel, a second unwinder adapted to unwind a second reel, a joining device adapted to join a first ply belonging to the first reel with a second ply belonging to the second reel, the joining device including a first pulling bar is able to pull a flap of the first ply along a joining path with the second ply, a second pulling bar is adapted to pull a flap of the second ply along a joining path with the first ply, joining means configured to join, in a joining point along the joining path, the flap of the first ply with the second ply or the flap of the second ply with the first ply, first cutting means configured to cut the first ply or the second ply upstream of the joining point where the joint is performed between the first ply and the second ply, and second cutting means configured to cut the flap of the first ply or the flap of the second ply downstream of the joining point.