After your PMD bag is collected, your PMD arrives at the sorting centre, where it is further sorted into no less than 16 different material streams. But that's not possible if you stack packaging together, or put a buttoned bag filled with PMD in your blue bag. And then there is a chance that the collector will stick a refusal sticker on your PMD bag saying ‘Sorry, we couldn't collect your PMD bag’.
Suppose that, before you throw an empty plastic bag into the blue bag, you think: ‘I'll just fill that bag with PMD and once that bag is full, I'll button it up and throw it into the blue bag’. Seems like a no-brainer, and certainly handy if you don't have room in the kitchen to store a full blue bag. But if you seal that bag and throw it in the blue bag like that, that bag and the packaging inside it have no chance of being recognised in the sorting facilities. The same with a plastic container that you fill with PMD and seal. Result: although you do sort PMD in the blue bag, by doing so your PMD will not be recycled but incinerated.
Of course, you may collect your PMD in a smaller bag first, but once that bag is full, tip the collected PMD in that bag into the blue bag first, followed by the bag itself. This way, you will have put all your PMD loose in the blue bag and everything will be able to be further processed at the sorting facilities and afterwards at the recycling companies.
And what was that about stacking pots into each other? That presents the same problem. The sorting systems recognise packaging in various ways: near-infrared, technical properties (such as ferrous metal in the case of metal packaging), and so on. But as soon as you start stacking flower pots, yoghurt pots or other containers, they are no longer sorted correctly due to shape or weight. Again, your sorting efforts are then negated and those potted jars go to residue and consequently to incineration.
Want a handy overview of the sorting rules and the right actions to take for proper recycling? You can download it here.
Other doubts about sorting your waste? Fill in what you want to recycle at the top of this page and immediately get the right sorting instructions!