foil 3d according to fig4 b simultaneously a certain calibration may take place in the end portion as appears from fig5 in order to avoid too far projecting portions fig6 and 7 more closely and somewhat modified show the opening device indicated in fig1 with reference numeral 4 the opening device consists of two tearing notches 4a and 4b respectively of which the tearing notch 4a defines the produced opening whereas 4b defines a grip tongue which in the example is completely located within the tearing notch 4a reference numeral 4c is a hatched area in fig7 which indicates a lacquering between an outer suitably injection moulded top portion 9 forming an outer layer and provided with the above tearing notches 4a and 4b and an inner layer 10 having a desired tightness by this means the grip tongue 4d formed by the tearing notch 4b may be easily gripped this is further facilitated in that said grip tongue 4d is made thicker and provided with a nail ridge or gripping edge 11 the grip tongue 4e runs into a prong 4d which likewise is formed with said thicker material by this means said prong easily can pierce the inner plastic layer 9 when the grip tongue is forced upwardly.