In yesterday’s column, Answer Man waded into the recycling stream in Ocean City. Today, I want to explore a different recycling-related question, which came from Laura Johnson, who lives in a townhouse community in Gaithersburg.

She wrote: “Not long ago we were advised that we should not recycle plastic bags. Plastic containers are okay. So we put plastic bags in with the regular trash. That doesn’t make sense. Why are plastic containers okay but not bags? Don’t the plastic bags still end up in the rivers, lakes and oceans?”

It was Gertrude Stein who wrote “Rose is a rose is a rose.” Stein did not write “Plastic is plastic is plastic.” If she had, she would have been wrong. Plastic comes in all sorts of varieties. It can’t all go together in the same hopper to be recycled.

Many consumers, said Susan Collins of the National Recycling Coalition, don’t understand “how delicate the balance of material in the manufacturing process is and how perfect the material input needs to be in order to make a product that’s of some value.”

Plastic carrier bags of the sort you get from a grocery store are made from a different type of resin than a plastic bottle or a yogurt cup.

“Those distinct differences are important because [the items are] used in different ways,” Collins said. “A plastic cup is both brittle and it can hold a form. Meanwhile, you want your carrier bag to be very, very flexible.”

Because they are born differently and live different lives, bottles and bags are handled differently at the end of their lives. Plastic bags are recyclable (we’ll see how shortly) but the processors who purchase them require them to be perfectly clean, said Adam Ortiz, director of Montgomery County’s Department of Environmental Protection.

“When they get mixed into the commingled recycling stream, they get dirty,” Ortiz said. A plastic container, on the other hand, gets shredded, then washed, then processed into pellets and reused.

That’s why you should never bundle your plastic, glass and metal recycling in a plastic bag and throw it all in a recycling bin.

But there’s a second, just as important, reason local jurisdictions don’t want plastic bags in with your recycling: They gum up the works.

A transfer station — the place where the recycling goes to be sorted — may seem like a big, stinky factory, but it’s actually a complex and delicate machine, crisscrossed with conveyor belts, screens and sorting tables.

“Plastic bags and other film-like plastics get caught in the machinery and jam it or are a fire hazard,” Ortiz said. “But people should not lose hope. They can just take clean bags back to the grocery store. All the major grocery retailers have drop-offs, usually right in the front.”

Most chain grocery stores will accept clean carrier bags and newspaper bags for recycling. Collins said you should not include “crinkly” plastic of the sort that holds prewashed salad.

It makes sense for the stores to serve as collection points for bags since they distribute so many and also because they handle so much plastic themselves, in the form of the sheeting that enshrouds bulk deliveries.

“Grocery stores are already handling that type of film plastic back-of-store,” Collins said.

A spokesperson for Giant said all of the plastic bags that are collected at its stores in the Washington area are put on a trailer and sent to the chain’s own recycling facility, along with cardboard, metal and other recyclable plastics that enter the store with its inventory.

The plastic bags are placed in a large baler and compressed into bales. The bales are shipped to Winchester, Va., where a miraculous transformation takes place.

The plastic bags are used by Trex, the company that pioneered “wood-alternative” building materials. The bags are cleaned, ground into granules and added to sawdust from reclaimed wood. That mixture is heated until it’s gooey and then pressed into decking, railings and outdoor furniture. The company says the average 500-square-foot composite Trex deck contains 140,000 recycled plastic bags.

That means you can be reading the newspaper on a Trex deck, knowing the bag it came in might end up in another deck someday.