Rubber or Cork? That is the question. There are merits with either, the traditionalist may prefer Cork because . . . . well, it's Cork. On the other hand Rubber lasts and lasts and lasts, is easily reconditioned to a new state with mild steriliser, and it's less likely to allow air ingress or absorbtion of unwanted liquids, either way in a head to head - Rubber Vs. Cork suitability test . . . . one of them will definitely win.