How to Effectively Block/Shield Passport Card RFID?
 

The instructions put out by the U.S. State Dept said to keep the Passport card in an RFID protective sleeve. If I keep my Passport card between 2 metal credit cards such as AmEx Platinum, Gold, or Chase Sapphire Reserve, would that be as protective from RFID skimming as using a protective sleeve?

No. The RFID will still be transmitting and will find a way out from between the two cards. It will be much more difficult for anyone to pick up the information since all of those cards you listed have their own RFID emissions. If you are concerned about it I would consider an RFID blocking wallet or purse.

I'm using the Apple MagSafe Wallet. One side (backside) of the MagSafe wallet is shielded against magnetism so the mag stripe on credit cards doesn't get de-activated, but I read shielding against magnetism also shields against RFID?

Apple's info on the MagSafe Wallet is unclear regarding RFID: "The leather wallet supports up to three cards and is shielded so it’s safe for credit cards."

According to everything I've read, the RFID chip in a passport card contains no PII, only a unique identifying number. So personally I've never taken any extraordinary precaution with my passport card.

However, I do routinely use an aluminum wallet/card case which blocks RFID signals from my various ID badges. If I were concerned about protecting my passport card, I'd keep it in my aluminum wallet, along with my various other IDs and cards. I like those wallets mostly for the convenience, small format, and easy access to the cards, but the RFID blocking is a side benefit.

The more physically all-encompassing the shielding is that is being used as a de facto Faraday cage, the more effective the shielding is likely to be to protect the RFID chip from being scanned.

While it's possible to use say separated towers of sorts to get some of the same blocking benefits as a box/bag used as a Faraday cage, there is a reason why government-secured electronic devices at risk of remote wiping by RF contact are placed in Faraday boxes/bags and not merely between just two planes of material for RF interference.

If you wrap a portable radio in tinfoil, you’ll hear the station go to static. You need something metallic completely covering the wallet to block RFID.

How effective are wallets like this? Is there a difference to the RFID on credit cards to passport cards and the like? I suspect so but haven't done any research myself at the moment.

Passport Card can work while you’re sitting in your car at a C&BP lane. Idk if credit cards could be read at that range. Payment devices can only read credit cards if up close, but I think that’s the payment device limiting itself.