Why is aluminum foil considered to Block RFID?

Aluminum foil is a conductor of electricity. Almost any conductor blocks radio waves because radio waves are a form of electromagnetic radiation. Conducting materials convert waves of electromagnetic radiation into thermal energy. Electromagnetic waves that hit the conductive material are partially reflected and partially refracted. So part of the wave may be heading back to you.

RFID blocking with aluminum foil. What are the disadvantages?

So, can aluminum foil block RFID?  Aluminum foil only reduces the effectiveness of card readers and interferes with the performance of the card being read. Which is why people assume it works generally. Tin foil does not block RFID, it only prevents reading the information from long distances. It doesn’t seem to be a foolproof protection method.

Regular aluminum foil (kitchen foil) or EMC static bags etc have no specific ability to block RFID, it is not designed to do this, it is simply one of the natural characteristics of aluminum.