A packaging line for products in bags, comprising: - a feed unit, configured to receive a web to from a reel and for moving it along a feed path; - a control unit, connected to the feed unit for moving the web intermittently, by a succession of forward movements of predetermined spacing; - a folding station, configured for folding the web about a folding line oriented along the feed path, for superposing a first and a second flap of the web; - a sealing station, configured for sealing the first and second flap of the folded web, along sealing lines oriented transversely to the folding line; - a cutting station, configured for cutting the packaging web and defining a plurality of packaging bags; - a filling station, configured for filling with a product the plurality of packaging bags; - a sealing station, configured for sealing the plurality of packaging bags; wherein the feed unit includes - a first motor-driven roller, controlled by the control unit for moving the web through the folding and sealing stations, by a first succession of forward movements, with a first feed step; - a second motor-driven roller, controlled by the control unit for moving the web by a second succession of forward movements different to that of the first succession of forward movements, with a second feed step, the second motor-driven roller being positioned downstream of the first motor-driven roller, for moving the web through the cutting station; - an adjustment unit, positioned between the first and the second motor-driven roller and configured for adjusting a tension of the web, characterised in that the adjustment unit includes: - a tensioning element, movable between a first operating position operatively in contact with the web, wherein the feed path has a first length, and a second operating position operatively in contact with the web, wherein the feed path has a second length different from the first length; an actuator, connected to the tensioning element for varying a position of the tensioning element between the said first and second operating positions (P1, P2), so as to vary the length of the feed path, and wherein the control unit is configured for receiving working data, representing the first and a second succession of forward movements, and for generating control signals, for controlling the actuator as a function of the working data. - a feed unit, configured to receive a web to from a reel and for moving it along a feed path; - a control unit, connected to the feed unit for moving the web intermittently, by a succession of forward movements of predetermined spacing; - a folding station, configured for folding the web about a folding line oriented along the feed path, for superposing a first and a second flap of the web; - a sealing station, configured for sealing the first and second flap of the folded web, along sealing lines oriented transversely to the folding line; - a cutting station, configured for cutting the packaging web and defining a plurality of packaging bags; - a filling station, configured for filling with a product the plurality of packaging bags; - a sealing station, configured for sealing the plurality of packaging bags; - a first motor-driven roller, controlled by the control unit for moving the web through the folding and sealing stations, by a first succession of forward movements, with a first feed step; - a second motor-driven roller, controlled by the control unit for moving the web by a second succession of forward movements different to that of the first succession of forward movements, with a second feed step, the second motor-driven roller being positioned downstream of the first motor-driven roller, for moving the web through the cutting station; - an adjustment unit, positioned between the first and the second motor-driven roller and configured for adjusting a tension of the web, - a tensioning element, movable between a first operating position operatively in contact with the web, wherein the feed path has a first length, and a second operating position operatively in contact with the web, wherein the feed path has a second length different from the first length; an actuator, connected to the tensioning element for varying a position of the tensioning element between the said first and second operating positions (P1, P2), so as to vary the length of the feed path, and wherein the control unit is configured for receiving working data, representing the first and a second succession of forward movements, and for generating control signals, for controlling the actuator as a function of the working data.