Two neighbouring councils frequently accept different materials in the same coloured bin, and residents reasonably read this as incompetence. The rules follow markets rather than principles.
Recycling is a commodity business
Collected material only becomes recycling when somebody buys it as an input, so the question a council answers is not whether an item can be recycled but whether the sorted output has a buyer.
Prices for baled paper, aluminium, glass cullet and mixed plastics move constantly, and a material that pays for its own processing one year may cost money to handle the next.
Collections are therefore adjusted to whatever the local processor can actually sell, which is why lists change without any change in the material itself.
The sorting facility sets the boundaries
Mixed collections are separated mechanically using screens, magnets, air jets and optical scanners, and each facility has a specific combination of that equipment.
An item that one plant can separate reliably may pass straight through another, ending up as contamination in a bale that then sells for less or is rejected.
Because facilities are built at different times to different specifications, the same item is genuinely recyclable in one town and genuinely not in the next.
Contamination is the expensive failure
A single wrong material can downgrade an entire load, and heavily contaminated loads are rejected and sent for disposal at the council's cost.
Councils therefore write conservative rules, excluding items that are technically recyclable but frequently confused with things that are not.
Optimistic sorting by residents, sometimes called wishful recycling, makes this worse, since one hopeful item can carry a real cost through the whole load.
Plastics are the hardest category
Plastic is not one material but a family of resins that cannot be melted together, and separating them requires identifying each item accurately at speed.
Bottles are relatively easy because their shape and resin are consistent, while films, trays and multi-layer packaging are difficult and often worth nothing when sorted.
The recycling symbols printed on packaging identify the resin rather than promising local acceptance, which is a persistent source of confusion.
Contracts lock rules in for years
Waste services are procured on long contracts, and the material list is written into an agreement negotiated years before residents encounter it.
Changing what is collected mid-contract means renegotiating with the operator, and possibly with the reprocessor beyond them.
Deposit return schemes and producer responsibility rules shift the economics again, which is why the rules on the bin will keep changing rather than settling.