Unwinder for web material, comprising: a first reel holder configured to support a first reel of web material; a second reel holder configured to support a second reel of web material; a dynamic storage device comprising: - a fixed frame; - at least one first return roller, preferably a plurality of first return rollers, mounted on the fixed frame; - a carriage mounted on a guide of the fixed frame and free to move along the guide moving towards or away from the first return roller; - at least one second return roller, preferably a plurality of second return rollers, mounted idle on the carriage; wherein said at least one first return roller and said at least one second return roller define a zigzag path for the web material unwinding from the first reel holder or from the second reel holder; a junction device disposed between the first reel holder or the second reel holder and the dynamic storage device and configured to splice an end portion of the web material running low on the first reel to an initial portion of the web material of the second reel or vice versa; an actuator located downstream of the dynamic storage device and configured to pull the web material; characterized in that the dynamic storage device comprises at least one motorized shaft, preferably a plurality of motorized shafts, mounted on the fixed frame, wherein said at least one first return roller is free to rotate on said at least one motorized shaft or wherein each first return roller is free to rotate on the respective motorized shaft. a first reel holder configured to support a first reel of web material; a second reel holder configured to support a second reel of web material; a dynamic storage device comprising: - a fixed frame; - at least one first return roller, preferably a plurality of first return rollers, mounted on the fixed frame; - a carriage mounted on a guide of the fixed frame and free to move along the guide moving towards or away from the first return roller; - at least one second return roller, preferably a plurality of second return rollers, mounted idle on the carriage; - a fixed frame; - at least one first return roller, preferably a plurality of first return rollers, mounted on the fixed frame; - a carriage mounted on a guide of the fixed frame and free to move along the guide moving towards or away from the first return roller; - at least one second return roller, preferably a plurality of second return rollers, mounted idle on the carriage; wherein said at least one first return roller and said at least one second return roller define a zigzag path for the web material unwinding from the first reel holder or from the second reel holder; a junction device disposed between the first reel holder or the second reel holder and the dynamic storage device and configured to splice an end portion of the web material running low on the first reel to an initial portion of the web material of the second reel or vice versa; an actuator located downstream of the dynamic storage device and configured to pull the web material; characterized in that the dynamic storage device comprises at least one motorized shaft, preferably a plurality of motorized shafts, mounted on the fixed frame, wherein said at least one first return roller is free to rotate on said at least one motorized shaft or wherein each first return roller is free to rotate on the respective motorized shaft.