There can be a total of five layers for packing (RFID tagging). The diagram below depicts these five levels. Each layer is then described in detail below the diagram.

Layer 5: Movement Vehicle (truck, aircraft, ship, train).

Layer 4: Freight container (20 or 40 foot Sea Vans, 463L Pallets with net).

Layer 3: Unit Load (Warehouse pallet, tri-wall packaging, commercial fiberboard packaging): One or more transport units or other items held together by means such as pallet, slip sheet, strapping, interlocking, glue, shrink wrap, or net wrap, making them suitable for transport, stacking, and storage as a unit. In distribution, an item or assembly of items assembled or restrained for handling and transportation as a single entity.

Layer 2: Transport Unit (cartons, boxes - second level packaging): Packaging designed to contain one or more articles or packages or bulk material for the purposes of transport, storage, handling and/or distribution.

Layer 1: Package (first level packaging - the "bubble pack"): The first tie, wrap or container of a single item or quantity thereof that constitutes a complete identifiable pack. A product package may be an item packaged singularly, multiple quantities of the same item packaged together or a group of parts packaged together.

Layer 0: Product item (individual item): A first level or higher assembly that is sold in a complete end-useable configuration.

Source: Background on the Use of RFID in the DOD Supply Chain: Attachment 1 - Background and Requirement for RFID in the DOD Supply Chain.