Glass is infinitely recyclable, so it’s easy to imagine that the bottles and jars you put out at the curb every week are headed off to be melted down and remade — baby-food jar into baby-food jar, beer bottle into beer bottle, forever and ever, amen. But not in Denver, or in many other Colorado communities with single-stream recycling, where everything from paper to plastic to glass is thrown into the same bin. Instead of being endlessly recycled, the glass that Denver residents put in their purple bins is reused only once, as a liner for landfills.

Surprised? That’s understandable. The city doesn’t draw attention to the fact — and hasn’t since it became the first place in Colorado to switch to single-stream recycling in 2005, in an effort to get more residents to participate. “Single-stream itself is a very positive thing,” says Eric Heyboer of the Colorado Department of Public Health and Environment. “When you make it really convenient for people to recycle, they will recycle more.”

But convenience on one end creates more work on the other. The stuff that’s collected in the single-stream process must be sorted so that the paper, plastic and aluminum can go their separate ways. While the workers and machines at recycling facilities can separate the junk mail from the yogurt tubs and pop cans, they have a harder time picking out the glass.

That’s because it’s broken. Between your curb and the recycling center, glass is jostled, dumped and smashed numerous times. By the end of the sorting process, it looks like recycling confetti: broken glass mixed with shreds of paper, bottle caps and other tiny detritus.