Can you try to confirm that NFC tags cannot be read through your material? It might be nice to have a little bag for something like this: https://www.bitmit.net/en/item/20291-3d-printed-nfc-enabled-bitcoin-simulacra
It will definitely block NFC which is usually around 13.56MH, the fabric should block that with about 80-90 dbi resistance, which should be more than enough to block signals. You could also double layer it for more protection too.
Thank you for your great question. Ill look into what it would take to make bags for that.