Abstract: A swim fin comprises a footpocket (1) and a propelling blade (2), which has a central longitudinal member (3) for supporting and stiffening the blade (2). The blade (2) has at least one pair, preferably a plurality, of ribs (5) oriented toward the free end (4) of the blade (2) and extending from the central longitudinal member (3) to the peripheral edge (4, 6) of the blade (2). The gaps (6) between the ribs (5) are at least partly closed by at least one waterproof element, so that the fin has an in-fluid behavior and an exterior aspect which is comparable to a plume or a bird's feather.

Abstract: The buckle (F) consists of a base part (F1), attached to one side of the footpocket of the fin (P) and comprising a movable strap-locking tooth (22), counteracting elastic means (24), associated to said tooth (22) and manual strap-releasing means (17) connected to said tooth, and of a strap-fastening part (F2), which only comprises strap-guiding means (13) for returning the strap (C), and is joined to the base part (F1), in such a way as to be able to slide in the longitudinal direction of the strap (C) between a retracted strap-tightening position, wherein it is automatically hooked to the base part (F1), so as to be manually releasable, and the strap-locking tooth (22) is engaged with the teeth (C1) of the strap (C), and a forward quick strap-loosening position, wherein the strap-locking tooth (22) is disengaged from the teeth (C1) of the strap and allows the latter to slide freely in both senses.