How Material Identification Codes Work
Recycling symbols on packaging are identification codes rather than a promise of acceptance in every collection scheme. Plastics use the numbered resin codes from 1 to 7, whose use on plastic products is defined by ASTM D7611, while metals follow their own system based on material abbreviations and, in some regions, two-digit material codes. The number inside a plastic triangle says what the polymer is; the aluminium equivalent says that the item is aluminium and should be routed into the metal stream.
Understanding that difference matters because packaging artwork, municipal guidance and sorting technology all rely on the same small set of marks. A symbol that is technically correct but printed below the resolution of a sorting camera has no practical value, which is why symbol size, contrast and placement are part of packaging design, not an afterthought.
The Codes Used for Aluminium
ALU: the material abbreviation printed or embossed on rigid aluminium packaging in most European markets to confirm that the item belongs to the aluminium fraction.
Code 41: the two-digit material identification code for aluminium packaging set out in European packaging material identification rules (Commission Decision 97/129/EC); other numbers in that system denote other materials.
Mobius loop or chasing arrows: the general recycling symbol used widely in North America. Used alone, it indicates recycling potential rather than a defined material.
Alloy series codes: some national marking schemes indicate the alloy family, for example a 1xxx, 3xxx or 5xxx series designation, so that plants can separate wrought grades before remelting.
Australasian Recycling Label: a symbol set combined with artwork and colour coding that tells consumers which component belongs in which bin.
China regulates the marking of plastics through GB/T 16288, which is a plastics numbering standard. Aluminium packaging is identified through material abbreviations and code systems instead, so the plastic numbering sequence should not be applied to metal packaging or copied into artwork as if it were interchangeable.
Symbols on Foil, Cans and Lids
Rigid bodies such as beverage cans and aerosol containers have enough surface area for a clear printed or embossed mark, and embossed marks survive shredding far better than ink. Lids, tabs and closures carry marks only where space and forming allow, so the material code is usually placed on the can wall or on the secondary packaging.
Clean foil may carry an ALU mark or a generic metal symbol, but many kerbside programmes still reject household foil because food contamination reduces recovery yield and small pieces fall through the sorting screens. Industrial recyclers do accept baled foil when it is labelled and reasonably clean. On laminates and pouches, the mark should identify the dominant material and the artwork should make it clear that a mixed structure may not be separated by the consumer.
Why Correct Labelling Matters
Sorting facilities separate aluminium from mixed packaging principally with eddy current separators, which eject conductive non-magnetic metals from the stream. A clear material code supports manual pre-sort, improves the accuracy of the automated line and keeps aluminium out of residue. Contamination is expensive in both directions: steel lids or glass left in an aluminium bale downgrade the melt, while aluminium that enters a paper or plastics stream can damage processing equipment.
Correctly marked aluminium also earns a better scrap price, because buyers can verify the material before purchase and avoid paying for a mixed bale. For brands, an accurate symbol protects the credibility of recyclability claims made on pack, since a claim that conflicts with the printed identification code is easy for regulators and consumers to challenge.
Emerging Identification Technologies
Several developments aim to push sorting accuracy beyond what a printed symbol can deliver. Digital watermarks embedded in artwork can be read by high-speed cameras across the whole pack surface, optical sorters now combine near-infrared sensors with machine vision to recognise shapes as well as materials, and tracer-based systems are used to route packaging back into food-grade streams.
Alongside these, embossed marks are being sized and positioned to survive shredding, and two-dimensional codes are used for recycled-content traceability so that a batch can be traced from collection to new product. Standardisation efforts continue, but the practical near-term improvement for most packaging is simpler: a legible, correctly placed material code on a mono-material pack.
Frequently Asked Questions
Q: What do the numbers 1 to 7 on packaging mean?
They are plastic resin identification codes: each number represents a polymer family such as PET, HDPE or PVC. The system describes plastics only and has no application to aluminium, which uses material abbreviations or its own code.
Q: Is the ALU symbol the same as code 41?
They identify the same material under different systems. ALU is a material abbreviation used on pack, while 41 is the two-digit aluminium code in the European packaging material identification system.
Q: Does the chasing arrows symbol mean an item will actually be recycled?
No. The chasing arrows mark indicates that the material is technically recyclable. Whether a specific item is collected depends on the local scheme, the pack size and whether it is clean enough for processing.
Q: Why do many kerbside programmes reject aluminium foil?
Mainly because of food contamination and piece size. Greasy foil burns during decoating and lowers recovery yield, and small fragments fall through the screens used to separate materials. Clean, scrunched foil is accepted in far more schemes.
Q: Does China use the plastic numbering system for aluminium packaging?
No. GB/T 16288 is a plastics marking standard. Aluminium packaging is instead identified through material abbreviations and material code systems, so artwork produced for plastic packs should not be reused unchanged for metal packs.
Q: How can packaging designers improve sorting accuracy?
Use a single material where possible, print or emboss a large, high-contrast material code on the largest face, place the mark where it remains visible after forming, and avoid full-body sleeves that hide the underlying material.
