How do I shield a card like Visa payWave and MasterCard PayPass to block its communication?
A piece of metal foil (any metal) adjacent (within a few mm) to the card will do it. It does NOT need to be wrapped round the card - close to the card on one side, and at least about a quarter of the area of the card will do fine as this will damp any read field. As the card is powered from the read field, you do not need to absorb anything like the same amount that you would for a conventional radio signal.