Actually, aluminum foil works as well as many of the RFID blocking materials on the market — not well at all. It will somewhat weaken the RFID signal across a very limited spectrum, but it will NOT prevent your cards and passports from being scanned through fabrics at a close range. We use a tested and certified RFID blocking material which exceeds industry standards for shielding all contactless credit cards, passports, drivers licenses, ISO 14443A/B and EPC Gen1/Gen2 contactless smart cards that operate at 13.56 Mhz and above (13.56 Mhz interface is the one that typically contains personal data).