Plastic cap and method of making the same

A plastic cap for a container (4), which cap (1), for oxygen-tight sealing of the container (4), comprises an oxygen-tight liner (8) to be joined to an opening end surface (6) of a spout (5) on the container (4) and, for attachment to the spout (5), has a circumferential skirt (2), which is arranged to surround the spout (5) and which has an internal annular bead (3) adapted for snap connection with a corresponding annular groove (7) in the spout (5), the liner (8) having an oxygen-tight intermediate layer (83), whose side facing the cap (1) is coated with a first plastic layer (81 ) arranged to be permanently joined to the cap (1) and whose side facing the container (4) is coated with a second plastic layer (82) arranged to be temporarily hermetically sealed to said opening end surface (6), and the liner (8) and the cap (1) being joined to each other such that the liner (8) when removing the cap (1) from the spout (5) accompanies the cap (1), wherein said first plastic layer (81) is arranged to be permanently joined, when injection-moulding the cap (1), to the plastic material of the cap (1), and that the skirt (2) at the end facing the container (4) has a radial projection (10), which serves as a thumb grip and which when opening the container (4) allows the cap (1) to be bent away from said opening end surface (6) so that the temporary, hermetic seal between the second plastic layer (82) of the liner (8) and the opening end surface (6) of the spout (5) is gradually broken.