Does a tag inside a wallet still read?
Often not, and the leather is rarely the culprit. Contactless bank cards, transport cards and metal plates share the space, and each one absorbs field or answers the reader itself. A wallet that fails is usually a wallet with too much in it.
The wallet itself is not the problem
Leather, fabric and plastic are insulators and the field passes through them. A tag alone in a wallet reads through the material with only the small loss that thickness costs.
So a wallet that fails is telling you about its contents rather than its construction, which is a more useful diagnosis than it first appears.
The other cards are
A contactless bank card is a tag in the sense that matters here: a coil and a chip that answers a reader. Put it next to your tag and two things happen.
It detunes your tag, because a second coil against the first shifts the tuning of both. And it answers the reader, so the phone sees more than one card in the field and cannot resolve which one you meant.
Transport cards, building access cards and hotel keys do the same. A wallet with three contactless cards in it is a difficult environment for a fourth.
The symptom is characteristic: the tag reads fine on its own, fails in the wallet, and works again when you take out one specific card.
Metal and blocking wallets
A metal money clip, a metal card, or a metal reinforcing plate cancels the field where it sits, which is total rather than partial.
Blocking wallets are built to do exactly this on purpose, using a conductive layer to stop cards being read without their owner's knowledge. They work, and they will stop your tag with the same efficiency.
If a wallet is advertised as protecting cards from scanning, it is not a place to keep a tag you intend to use.
Making it work
Take the card out. This is unglamorous and it is what most people end up doing, and it works every time.
Use a wallet with a separated outer pocket, so the tag is presented with nothing behind it. Some are designed for exactly this.
Keep the tag at the outside of the stack rather than the middle, and present that face to the phone. It does not solve a wallet full of contactless cards, and it helps in mild cases.
And test the actual wallet with the actual contents before handing cards to a team. A card that works in an empty wallet on a desk tells you nothing about the wallet it will live in.
Frequently asked questions
Why does my card work sometimes and not others?
Because it depends which way the wallet is turned and what sits between the tag and the phone. Position dependent behaviour points at other cards rather than at a faulty tag.
Will my bank card be damaged?
No. The cards interfere with each other's reading and neither is harmed, so normal behaviour returns as soon as they are separated.
Do blocking wallets damage tags?
No. They prevent reading while the tag is inside and change nothing about the tag itself.
Is a metal card a bad idea for a wallet?
It reads from one face only and it can disturb neighbours in a stack. Test the real combination rather than assuming it will behave like a plastic card.