Abstract: The invention concerns a plastic cap (1) and a container (4) using same. The plastic cap (1) comprises an oxygen-tight liner (8) to be joined to an opening end surface (6) of a spout (5) on the container (4). The cap (1) has a circumferential skirt (2) with an internal annular bead (3) adapted for snap connection with a corresponding annular groove (7) in the spout (5). The liner (8) has on the side facing the cap (1) a first plastic layer (81), which is arranged to be permanently joined, when injection-molding the cap (1), to the plastic material of the cap (1), and on the side facing the container (4) a second plastic layer (82), which is arranged to be temporarily hermetically sealed to said opening end surface (6).