A retractable mast for barriers comprising: - at least one fixed element, having an upper end and a lower end, said fixed element extending along a longitudinal axis (a) for a total extension; - at least one sliding element having an upper portion and a lower portion, said sliding element extending along said longitudinal axis (a) for a total extension; - at least one gap between the fixed element and the sliding element; said gap being defined by a radial distance, perpendicularly measured with respect to said longitudinal axis (a), said fixed element and said sliding element being coupled in such a way that the sliding element can be translated in the fixed element along said longitudinal axis (a), from a first position, in which it is housed in the fixed element, for a portion of at least 70% of its total extension, and a second position, in which it is extracted from the fixed element, for a portion of at least 50% of its total extension; said fixed element having at least one groove and said sliding element having at least one guide pin cooperating with said groove, wherein said groove has at least two branches (D1, D2), one of the two branches (D1, D2) being shorter than the other one, wherein the retractable mast has at least one sealing device, interposed between the fixed element and the sliding element; characterized in that - the average radial distance is less than 5 mm; - said fixed element has a duct, connecting the gap with the outside of said fixed element and said sliding element has at least one relief valve, connecting the inside of the sliding element with the gap, permitting the air exit during the sliding of said sliding element from said second position to said first position, said relief valve is placed in the upper part of the sliding element, above more than 50% of its total extension; - said sealing device has at least two sealing elements (15', 15"), made of waterproof material, and said fixed element has at least two housings (22', 22") for said at least two sealing elements (15', 15"), wherein said at least two sealing elements (15', 15") are substantially placed at the upper end of said fixed element and axially spaced along a direction parallel to the longitudinal axis (a), and wherein said at least two sealing elements (15', 15") seal said gap between said fixed element and said sliding element, while permitting the sliding of said sliding element with respect to said fixed element. - at least one fixed element, having an upper end and a lower end, said fixed element extending along a longitudinal axis (a) for a total extension; - at least one sliding element having an upper portion and a lower portion, said sliding element extending along said longitudinal axis (a) for a total extension; - at least one gap between the fixed element and the sliding element; said gap being defined by a radial distance, perpendicularly measured with respect to said longitudinal axis (a), - the average radial distance is less than 5 mm; - said fixed element has a duct, connecting the gap with the outside of said fixed element and said sliding element has at least one relief valve, connecting the inside of the sliding element with the gap, permitting the air exit during the sliding of said sliding element from said second position to said first position, said relief valve is placed in the upper part of the sliding element, above more than 50% of its total extension; - said sealing device has at least two sealing elements (15', 15"), made of waterproof material, and said fixed element has at least two housings (22', 22") for said at least two sealing elements (15', 15"), wherein said at least two sealing elements (15', 15") are substantially placed at the upper end of said fixed element and axially spaced along a direction parallel to the longitudinal axis (a), and wherein said at least two sealing elements (15', 15") seal said gap between said fixed element and said sliding element, while permitting the sliding of said sliding element with respect to said fixed element.