Channel

Amazon FBA Prep for Phone Cases: Polybags, FNSKU and the Rejections That Cost Most

22 October 2026

FBA prep is the cheapest part of a shipment to get right and one of the most expensive to get wrong, because a rejected carton does not travel back to the factory. It goes into a removal order or a disposal, and the units are gone either way.

The rules are not complicated. They are, however, applied at the carton level by a receiving clerk with a scanner, which means a single mislabelled unit in a carton can fail the whole carton.

Rule 1: the polybag rule that catches most sellers

If a polybag has an opening of 5 inches (127 mm) or more, it must carry a suffocation warning printed on the bag itself — not on a sticker, not on an insert. The standard wording is: "Warning: Plastic bags can be dangerous. To avoid danger of suffocation, keep this bag away from babies and children. Do not use in cribs, beds, carriages, or playpens. This bag is not a toy."

For a phone case the bag is usually 130 × 180 mm or larger, so the rule applies. Note the direction: an opening of 5 inches, measured as the opening, not the bag's diagonal.

Rule 2: the FNSKU covers the barcode, and only the barcode

Your retail UPC or EAN is on the packaging; the FNSKU is the Amazon label. The FNSKU must cover the manufacturer barcode completely, and must not cover the model name, the quantity, the regulatory panel or any warning. A case where the FNSKU sits across the bilingual panel is a compliance problem dressed as a labelling problem.

Rule 3: carton limits

Rule 4: multipacks and sets

A two-pack must be sold as one sellable unit: bagged together, or in a single box, with the FNSKU on the outside of the unit and not on each item. Bundling two separately barcoded units and taping them is the classic mistake — the receiving scan reads two units and the inventory is wrong from day one.

Rule 5: what "prep" actually includes

1. Polybag with the suffocation warning, sealed, with the air expressed.
2. FNSKU applied over the manufacturer barcode.
3. Unit counted into the carton against a packing list.
4. Carton sealed, weighed, labelled on two adjacent sides.
5. Carton marked with the box contents label if the shipment is a mixed carton.

Rule 6: who should do it

Factory prep only works if the factory receives the FNSKU label file and a written specification, and if somebody photographs the first prepped carton before the container closes. Shipping 20,000 units with the wrong barcode covering the wrong panel is a recovery measured in weeks.

What we need from you to prep to FBA standard

• FNSKU label file, at print resolution, with the label size.
• Confirmation of single unit or multipack, and the multipack bag or box specification.
• Carton label file, and whether labels are applied by us or by your prep centre.
• Whether the retail sleeve or a plain polybag is the sellable unit.
• Any market-specific panel — the Prop 65 warning for the US, the bilingual panel for Canada — resolved on the artwork before printing.

If the packaging itself is still open, the packaging article covers the dieline decisions that make FBA prep cheap instead of a per-unit surcharge.

Questions buyers actually ask

Do phone case polybags need a suffocation warning for FBA?

Yes, when the bag opening is 5 inches (127 mm) or more. The warning must be printed on the bag, not applied as a sticker, and a case-sized bag almost always crosses that threshold.

Where should the FNSKU go on a phone case?

Over the manufacturer barcode, on a flat area, without covering the model name, quantity, warnings or regulatory panel. Reserve that area in the dieline before printing.

Can the factory apply FNSKU labels?

Yes, and it is usually the cheapest route if you supply the label file and a written prep specification. Insist on photographs of the first prepped carton before the balance ships.