There are various RFID tags that are designed to work in close proximity to metal but generally they hope for free space or at least limited loading in close proximity.
As a work around for RFID tag sniffing various metallised wallets and card sleeves are available.
I am curious if anyone has insight into the best metal to select for making such a case?
Copper, aluminium, maybe gold and untarnished silver are good conductors. Mu-metal is a good magnetic field absorber. The MetGlas type materials have some funny characteristics and are used in fluxgate magnetometers and as far as I know the strange shop anti-theft tags with the two bits of foil inside.
Would the low frequency tags prefer a magnetic shield and the VHF and UHF tags prefer a conductive shield? Could or should one use both types to cover all of one's bases?
Personal privacy and bank card and passport sniffing are going to become more relevant in future. If I want to market protective wallets one day I would like to make them from the right stuff. Persons movements can be tracked, funds withdrawn and some of their identifying details may be visible to determined parties who are up to no good. Having a flexible shield is preferable but even a trustworthy hard case would be of use in many cases.
The Wallets would be like your everyday bill fold, bank card holder, purse or wallet. Basically any place that you might store your banking cards or card style biometric identity cards. A larger version that can hold passports and airline tickets would also be an option for travelers.