RFID tags for metal, liquids and apparel: how to choose

Readers get the attention, but the tag decides most RFID outcomes. A UHF tag is a chip plus an antenna tuned to work on a particular kind of material. Put a tag designed for cardboard on a steel toolbox or a bottle of water and it will read poorly or not at all — not because RFID “does not work on metal”, but because that tag was never designed for it.

A standard UHF inlay laid flat on metal is detuned by it. On-metal tags solve this by separating the antenna from the surface (foam or plastic spacers, flexible “flag” tags that stand off the surface) or by using the metal as part of the antenna (hard tags with a ground plane, ceramic or PCB tags). On-metal tags are thicker and cost more than paper inlays, but read well — often better than on cardboard.

• Tools and instruments — small rugged tags, sometimes embedded in a drilled pocket; check temperature and chemical resistance.
• Servers and IT kit — thin on-metal labels on the bezel or rail where the handheld can see them.
• Roll cages and returnable metal — rugged tags that survive impacts and washing.
• Cans and foil packs — a hard case for item-level; often tagged at case or pallet level instead.

Tagged servers and devices on a live data-center map

Water and water-rich products absorb UHF energy, so a tag on the side of a full bottle sees less signal. Work with the geometry: tag the cap or neck, use a hang tag that sits in air, or a tag designed for liquids. For small vials and lab samples read at close range, HF often works better — see UHF vs HF vs NFC.

Apparel is where item-level UHF RFID took off because it is RF-friendly: fabric barely affects the tag. The choice is mostly practical: a hang tag or price ticket with an inlay (removed at sale), an adhesive label on packaging, or a sewn-in care label for items that are tracked through laundries and rentals (wash-proof tags exist for that). Inlay size trades range against how small the label must be.

Shipping labels with an RFID inlay are printed and encoded in one pass by RFID printer-encoders. On pallets, tag at least two sides so a portal sees one whatever the orientation, and keep tags away from metal straps and liquid-filled layers. Encode an SSCC for logistics units and SGTIN for trade items, so every system agrees what a read means.

1. 1
   Shortlist three or four tags

   From datasheets matched to your materials and sizes.

2. 2
   Tag real products

   Your worst ones: metal, liquids, dense packs.

3. 3
   Read them the way you will

   With the handheld, portal or shelf reader you plan to use, at real distance and speed.

4. 4
   Record read rate, not just range

   Out of 100 passes or 100 items, how many were read? See RFID read rate.

Tags and readers we work with are on RFID hardware — e.g. from Zebra, Chainway, SATO or Sanray (trademarks of their owners). Once the tags read reliably, the reads go on a live map: see RFID tool tracking, the RFID IT asset audit and RFID for retail stores.