At the very least, paper & cardboard should be kept separate from plastic & aluminium. The first really need to be kept free of grease/dirt. Plastic/aluminium/

At the very least, paper & cardboard should be kept separate from plastic & aluminium. The first really need to be kept free of grease/dirt. Plastic/aluminium/steel can be separated relatively easy… but then comes the problem of plastics themselves, separating each type.