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 a mild steriliser solution and it's less likely to allow air ingress or absorbtion of unwanted liquids, either way in a head to head race . . . . one of them will definitely win!