Device for covering a surface comprising: (a) a substantially rectangular cover comprising an internal face and an external face which are separated from one another by the thickness of the cover, and having two longitudinal edges opposite one another and two transverse edges opposite one another, (b) a longitudinal strip comprising an interior edge being fixed to each longitudinal edge of the cover, and comprising an exterior edge which is free and equipped with a projecting bead extending along said edge, (c) a drum mounted with the ability to rotate able to roll up and unroll the cover, said drum being mounted on a mechanism for longitudinal translation along (d) rails designed to be positioned one on each side of said surface and each made up of a profiled section having an opening on one of its faces and facing away from the surface that is to be covered, said face comprising at least one adjacent flange situated on the side adjacent to the surface that is to be covered and partially closing said opening, said translation mechanism allowing longitudinal translation of the drum in a first direction that causes the cover to be unrolled and deployed over the surface that is to be covered with the internal face facing toward said surface and, in a second direction, that causes the cover to be rolled up and removed from said surface, (e) a deflection surface provided on each side of the surface that is to be covered so as to guide and position said bead of each longitudinal strip of the cover to face the opening in the corresponding rail as the drum effects the translational movement in the first direction causing the cover to unroll, (f) a system for continuously locking the bead of the longitudinal edges of the cover in the opening of said rails making it possible, once the bead has been engaged in the opening, to lock it by wedging it under the adjacent flange of the corresponding rail as the cover is gradually unrolled as the drum effects the translational movement in the first direction, and, as the drum effects the translational movement in the second direction, to release the bead, allowing it to disengage as the cover is gradually rolled up, characterized in that the cover comprises at least one flap (15e, 15i) extending along each of its longitudinal edges and able, when a portion of each bead is wedged under the adjacent flange of the corresponding rail, to isolate the portion of the longitudinal strip that corresponds to the trapped bead portion either from the atmosphere prevailing between the internal face of the deployed cover portion and the surface portion covered, or from solar radiation. (a) a substantially rectangular cover comprising an internal face and an external face which are separated from one another by the thickness of the cover, and having two longitudinal edges opposite one another and two transverse edges opposite one another, (b) a longitudinal strip comprising an interior edge being fixed to each longitudinal edge of the cover, and comprising an exterior edge which is free and equipped with a projecting bead extending along said edge, (c) a drum mounted with the ability to rotate able to roll up and unroll the cover, said drum being mounted on a mechanism for longitudinal translation along (d) rails designed to be positioned one on each side of said surface and each made up of a profiled section having an opening on one of its faces and facing away from the surface that is to be covered, said face comprising at least one adjacent flange situated on the side adjacent to the surface that is to be covered and partially closing said opening, said translation mechanism allowing longitudinal translation of the drum in a first direction that causes the cover to be unrolled and deployed over the surface that is to be covered with the internal face facing toward said surface and, in a second direction, that causes the cover to be rolled up and removed from said surface, (e) a deflection surface provided on each side of the surface that is to be covered so as to guide and position said bead of each longitudinal strip of the cover to face the opening in the corresponding rail as the drum effects the translational movement in the first direction causing the cover to unroll, (f) a system for continuously locking the bead of the longitudinal edges of the cover in the opening of said rails making it possible, once the bead has been engaged in the opening, to lock it by wedging it under the adjacent flange of the corresponding rail as the cover is gradually unrolled as the drum effects the translational movement in the first direction, and, as the drum effects the translational movement in the second direction, to release the bead, allowing it to disengage as the cover is gradually rolled up,