A closure assembly for a package with flexible thin-walled pouch for the containment of fruit juices and puree, yoghurt, energy drinks and the like, comprising: - a spout assembly comprising a connection portion, suitable for being hermetically applied to the pouch, and a threaded spout, externally provided with a ring seat; - a closure comprising a cap assembly comprising: a) a cap screwable to the spout; b) a guarantee seal to highlight the first opening of the closure, comprising: i) a guarantee ring at least partially received in the ring seat of the spout; ii) an annular guarantee band which, in an unbroken seal configuration, axially overlaps the guarantee ring, separated from the guarantee ring by a first separation line and from the cap by a second separation line; iii) a plurality of breakable bridges which, in the unbroken seal configuration, join the guarantee ring to the guarantee band and the guarantee band to the cap; iv) a first attachment portion, more resistant than the bridges, which joins the guarantee band to the guarantee ring and a second attachment portion, more resistant than the bridges, which joins the guarantee band to the cap; - wherein, in an open configuration of the closure in which the cap is unscrewed and the bridges are broken, the guarantee band forms a strap which keeps the cap fastened to the guarantee ring; - said guarantee band having a length such that, in a use configuration in which the guarantee band is stretched, the second attachment portion is axially arranged below the connection portion of the spout assembly; wherein the guarantee band extends between an initial portion and an end portion, and, in the unbroken seal configuration, the initial portion is circumferentially adjacent to, and spaced apart from, the end portion; characterised in that the guarantee seal comprises a predominantly circumferentially extending breakable segment joining the initial portion of the guarantee band with the end portion, wherein, in the open configuration, the breakable segment is broken. - a spout assembly comprising a connection portion, suitable for being hermetically applied to the pouch, and a threaded spout, externally provided with a ring seat; - a closure comprising a cap assembly comprising: a) a cap screwable to the spout; b) a guarantee seal to highlight the first opening of the closure, comprising: i) a guarantee ring at least partially received in the ring seat of the spout; ii) an annular guarantee band which, in an unbroken seal configuration, axially overlaps the guarantee ring, separated from the guarantee ring by a first separation line and from the cap by a second separation line; iii) a plurality of breakable bridges which, in the unbroken seal configuration, join the guarantee ring to the guarantee band and the guarantee band to the cap; iv) a first attachment portion, more resistant than the bridges, which joins the guarantee band to the guarantee ring and a second attachment portion, more resistant than the bridges, which joins the guarantee band to the cap; a) a cap screwable to the spout; b) a guarantee seal to highlight the first opening of the closure, comprising: i) a guarantee ring at least partially received in the ring seat of the spout; ii) an annular guarantee band which, in an unbroken seal configuration, axially overlaps the guarantee ring, separated from the guarantee ring by a first separation line and from the cap by a second separation line; iii) a plurality of breakable bridges which, in the unbroken seal configuration, join the guarantee ring to the guarantee band and the guarantee band to the cap; iv) a first attachment portion, more resistant than the bridges, which joins the guarantee band to the guarantee ring and a second attachment portion, more resistant than the bridges, which joins the guarantee band to the cap; i) a guarantee ring at least partially received in the ring seat of the spout; ii) an annular guarantee band which, in an unbroken seal configuration, axially overlaps the guarantee ring, separated from the guarantee ring by a first separation line and from the cap by a second separation line; iii) a plurality of breakable bridges which, in the unbroken seal configuration, join the guarantee ring to the guarantee band and the guarantee band to the cap; iv) a first attachment portion, more resistant than the bridges, which joins the guarantee band to the guarantee ring and a second attachment portion, more resistant than the bridges, which joins the guarantee band to the cap; - wherein, in an open configuration of the closure in which the cap is unscrewed and the bridges are broken, the guarantee band forms a strap which keeps the cap fastened to the guarantee ring; - said guarantee band having a length such that, in a use configuration in which the guarantee band is stretched, the second attachment portion is axially arranged below the connection portion of the spout assembly; wherein the guarantee band extends between an initial portion and an end portion, and, in the unbroken seal configuration, the initial portion is circumferentially adjacent to, and spaced apart from, the end portion; characterised in that the guarantee seal comprises a predominantly circumferentially extending breakable segment joining the initial portion of the guarantee band with the end portion, wherein, in the open configuration, the breakable segment is broken.