A closure for a spout of a flexible thin-walled packaging, comprising: - a cap comprising an annular cap wall having a central cap axis which extends between a cap lower end and a cap upper end, for which a main plane of symmetry is defined through the cap axis, wherein the cap is internally threaded to be suitable for screwing onto a thread of the spout; - a tamper-evident seal comprising a tamper-evident ring suitable for being applied to the spout, an annular tamper-evident band placed between the tamper-evident ring and the cap lower end of the cap and a plurality of breakable bridges which join the tamper-evident band to the tamper-evident ring and the cap, wherein the tamper-evident band extends between a first end permanently joined to the cap and a second end permanently joined to the tamper-evident ring to form a tie between the cap and the tamper-evident ring; - a grip surface for gripping the closure, comprising an annular grip surface wall which is coaxial to the cap axis, surrounding the cap wall and radially arranged spaced apart therefrom, which axially extends from a lower end to an upper end, wherein the grip surface wall has, at the lower end, an undulated grip surface edge made up of a succession of low sections and high sections that are joined to each other, such as to create bulges (72, 74) and windows (76, 78) of the grip surface, in circumferential sequence; - wherein a first window of said windows (76, 78) is circumferentially delimited by a limit section of the grip surface edge belonging to a first bulge of said bulges (72, 74), and by a limit section of the grip surface edge belonging to another bulge of said bulges (72, 74); - wherein a first window plane tangent to the first limit section and parallel to the main plane of symmetry and a second window plane tangent to the second limit section and parallel to the main plane of symmetry are defined for said first window; - wherein the cap and the tamper-evident seal are contained in width between said window planes (P4, P5); - wherein an imaginary plane orthogonal to the cap axis is tangent inferiorly to the low section of the grip surface edge, which axially delimits inferiorly at least one of said bulges (72, 74); - and wherein said imaginary plane is arranged axially below the lower cap end of the cap wall. - a cap comprising an annular cap wall having a central cap axis which extends between a cap lower end and a cap upper end, for which a main plane of symmetry is defined through the cap axis, wherein the cap is internally threaded to be suitable for screwing onto a thread of the spout; - a tamper-evident seal comprising a tamper-evident ring suitable for being applied to the spout, an annular tamper-evident band placed between the tamper-evident ring and the cap lower end of the cap and a plurality of breakable bridges which join the tamper-evident band to the tamper-evident ring and the cap, wherein the tamper-evident band extends between a first end permanently joined to the cap and a second end permanently joined to the tamper-evident ring to form a tie between the cap and the tamper-evident ring; - a grip surface for gripping the closure, comprising an annular grip surface wall which is coaxial to the cap axis, surrounding the cap wall and radially arranged spaced apart therefrom, which axially extends from a lower end to an upper end, wherein the grip surface wall has, at the lower end, an undulated grip surface edge made up of a succession of low sections and high sections that are joined to each other, such as to create bulges (72, 74) and windows (76, 78) of the grip surface, in circumferential sequence; - wherein a first window of said windows (76, 78) is circumferentially delimited by a limit section of the grip surface edge belonging to a first bulge of said bulges (72, 74), and by a limit section of the grip surface edge belonging to another bulge of said bulges (72, 74); - wherein a first window plane tangent to the first limit section and parallel to the main plane of symmetry and a second window plane tangent to the second limit section and parallel to the main plane of symmetry are defined for said first window; - wherein the cap and the tamper-evident seal are contained in width between said window planes (P4, P5); - wherein an imaginary plane orthogonal to the cap axis is tangent inferiorly to the low section of the grip surface edge, which axially delimits inferiorly at least one of said bulges (72, 74); - and wherein said imaginary plane is arranged axially below the lower cap end of the cap wall.