I can't say if it actually works as nobody tried to steal my data, just swiped in front of the proxy card reader and it picks up the signal from card and let me through the door! The proxy card is on the inner flap of the wallet, not on the outer flap itself, so behind as many layers as possible. I probably wouldn't recommend this as I don't trust it to block RFID readers when the proxy card is so easy to read.
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