The regular rfid Tags or rfid labels don’t work if placed on metal. These special rfid tags can be applied on the metal surfaces, because they are with a layer of ferriee that protects the magnetic fiels.

Do you know why the rfid tags can not work on the metal?
Because RFID Tags work by electromagnetic induction, metal inviroment can interfere the it and reduces the performance of the RFID TAGS’s antenna,effectively and stopping it creating the current needed to power the chup. Then we use a specail "an-ti metal" layer on the tag. It is a ferrite foil barrier between the tag and the adhesive layer.
So we called it on-metal rfid tags or Anti-metal rfid tag.

OPP IOT Technologies Co., Ltd is a professional on-metal/Anti-metal tag supplier,Our on-metal/Anti-metal tag is designed for tagging metal objects and surfaces, as well as challenging non-metal objects. The thin, soft and fl exible tag structure ideally suits curved and fl at surfaces, and offers converters huge opportunities to create attractive solutions for end users.

Parts of our On-metal tags / Anti-metal tags as follow:
http://www.oprfid.com/RFIDTag-antimetallabel.html
http://www.oprfid.com/UHF-metal-label.html
http://www.oprfid.com/High-temperature-UHF-Metal-tag.html
http://www.oprfid.com/fr4-uhf-metal-tag.html
http://www.oprfid.com/mini-uhf-metal-tags.html
http://www.oprfid.com/long-distance-uhf-metal-tag.html