Dear Recyclebank: When I don't know if something's recyclable, I usually put it in the recycling bin. I hear that's bad, but I don't understand why. If recycling gets sorted by type of material before being sold off to manufacturers, why does it matter if I put unaccepted things in my recycling bin? Won't they just get sorted out anyway, and possibly even get recycled? –Walt S.

Dear Walt: The simplest answer is that sorting takes time and costs money. Materials coming through the MRF can be sorted by machinery or by hand; usually it’s a combination of both. Either way, unusable materials (called recycling contamination) slow down the sorting process and require the facility to take on the burden of excess waste disposal to landfills, thus making recycling more expensive for everyone.

Much of the issue with contamination goes beyond a simple sort. MRFs are not just separating materials into bales by material type and piles of what should get trashed — they are responsible for creating high quality bales that they can sell to manufacturers. And individual items at a MRF don’t exist in a vacuum from each other: The wrong sort of plastic can affect the final quality — and therefore value — of a whole batch of plastic recycling, or even ruin it entirely. Likewise, an item with food residue can contaminate an entire batch of paper recycling. And where there’s more contamination to sort out, there’s more room for error, more bales with lower value, and more entirely unsellable bales, which usually end up in landfills.

Keep in mind, too, that an item’s material may not be what’s hampering its recyclability; it could be that the local MRF’s machinery can’t process a specific item’s shape or size. For instance, you may look at a plastic bag and think “Plastic’s recyclable, so I’ll put it in my bin,” but thin films get caught in most common MRF machines, causing the process to grind to a halt until they can be removed (costing time and money!).

The moral of the story? Contamination has a real impact on both landfills and pocketbooks. It can be confusing to keep up with what’s recyclable and what isn’t, but it’s important to take personal responsibility for your part in the process. When you’re unsure about something, take the time to double-check your local facility’s guidelines, or err on the side of caution: When in doubt, throw it out.