Newspapers, milk jugs, glass bottles, aluminum or tin cans. Most people know that those items can be recycled. But what else should go in your curbside bin? Which items can cause damage if you mistakenly toss them in? And what are the odds that your “recyclable” plastic will get recycled? Here’s the low-down.

1. Don’t “wish-cycle.”

Unsure if you can recycle your plastic bags or shredded documents?

“I get it,” says Lynn Hoffman, co-president of Eureka Recycling, a zero-waste organization in Minneapolis.

“There’s no information on the product, maybe it looks similar to something else that you know goes in the bin, so you toss it in.”

That’s called “wish-cycling,” and it isn’t harmless.

“The risk is that it can contaminate other recyclables, damage equipment, and cause major safety issues for your recycler,” says Hoffman.

“We have to shut down our equipment for a couple of hours each day while our staff climbs in with box cutters to cut out plastic bags, hoses, extension cords, and other materials. We spend about $75,000 a year doing that.”

And it makes recycling more expensive. Even if your shredded paper doesn’t cause damage, hauling it first to a recycling facility and then to a landfill or incinerator wastes fuel and person-power.

“When in doubt, find out what your local program accepts in your curbside bin,” says Hoffman.

2. Most plastic never gets recycled.

What makes plastic desirable for manufacturers—it comes in many varieties, it’s durable, etc.—is exactly why it’s a recycling nightmare.

“There are thousands of types of plastic, all with different colorants and additives that are difficult or impossible to tease apart,” says Judith Enck, president of Beyond Plastics, a project at Vermont’s Bennington College that aims to end plastic pollution.

What’s more, plastic gets “down­cycled.” That is, it becomes an inferior version of itself each time it’s recycled.

“Plastic is incredibly difficult to recycle,” says Enck. “And that’s partly why the plastic recycling rate is an abysmal 5 to 6 percent.”

How can that be, when everything from yogurt containers to Styrofoam takeout boxes has a recycling symbol?

“Those are resin identification codes that identify the type of plastic the product is made of,” explains Enck. “You should not interpret that symbol as meaning that the material has a fighting chance of being recycled.”

The symbols have done more for the plastics industry than for the planet.

“Adding prominent recycling symbols on packaging was a big greenwashing move by companies because people feel better about buying stuff they think they can recycle,” says Hoffman.

“You toss it in your bin thinking that something good is going to happen to it, but that’s not true of most plastic.” Most ends up in a landfill.

“Plastics are numbered 1 through 7, but there are really only markets for No. 1 and No. 2,” says Enck. “Some communities have markets for No. 5, but very few.”

[Click here to see examples of the types of plastic with each number.]

And companies like Trex use plastic bags (No. 4) collected by store take-back programs to create composite lumber for building decks, benches, and more. But that’s still a tiny fraction of the plastic bags, wraps, and film we discard.

“Using less plastic is always better, ” says Hoffman, “because of growing concerns about any plastic shedding chemicals and microplastics into our soil and water.”

To make it easier on consumers, many recycling collectors will take plastics with any number. But “collection does not mean recycling,” Enck points out.

And don’t be fooled by packaging that says something like “check locally.”

“That’s another industry ploy that puts the burden on local governments,” says Enck. “‘Not recycled in all communities’ usually means ‘not recycled.’”

“We cannot recycle our way out of the plastic pollution problem,” notes Enck.

Instead, we need to use less. That starts with holding corporations accountable for the plastic they produce.

3. Glass and metal: recycling’s poster children.

Unlike plastic and paper, glass and metal don’t lose quality when recycled. “We consider them infinitely recyclable,” says Hoffman.

What’s more, “the energy savings to make a bottle or can from recycled materials instead of from raw materials are substantial.”

But you shouldn’t recycle all metal and glass.

“Scrap metal, which is basically non-can metal, doesn’t belong in your curbside recycling bin,” says Hoffman.

“Pots and pans, nails, knives, and ammunition all wreak havoc on our machinery.” Take them to a local scrap-metal recycler instead.

And keep glass dishes, windows, and mirrors out of your recycling bin. They’re made of a different kind of glass than jars and bottles.

4. Cartons are complicated.

Wondering what to do with your empty milk carton? Great question.

All cartons that hold liquids—whether refrigerated or shelf-stable—are mostly paperboard lined with plastic. But the shelf-stable cartons also have a layer of aluminum foil that keeps out oxygen and light.

At some facilities, both types of cartons get shredded and turned into building materials like roofboard. At others, special equipment separates the paper from the plastic and foil, which likely end up as trash. No facility turns recycled cartons into new cartons.

If your recycler accepts cartons, toss them in the bin. But keep in mind that they may not be as green an option as they seem. There aren’t many carton recycling centers, so your cartons may be traveling far or headed to a landfill.

5. Recycling isn’t broken.

“There’s been a lot of bad press around recycling,” says Hoffman. “But recycling isn’t broken. It’s an important component of sustainability. It’s just not going to fix our problems with consumption.”

We need to first reduce, then reuse, then, finally, recycle our materials.

“In our facility alone, we keep 400 tons a day out of the landfill or incinerator,” says Hoffman. “Instead, it goes back into the supply chain so that we don’t have to extract or frack more or cut down more trees.”

“Don’t get discouraged,” she adds. “If you’re recycling things like aluminum cans, glass and plastic bottles, and paper, you’re doing a really good thing.”