On a recent Saturday afternoon, I went to a clothing swap hosted by a group known as the Brooklyn Clothing Exchange.

For an exchange of second-hand clothing, the setting was sublime: The Macon branch of the Brooklyn library system, located in the neighborhood of Stuyvesant Heights, is a stately and gorgeous Classic Revival red-brick building erected more than a hundred years ago as a gift from Andrew Carnegie. Of course, the swap meet was held in its ancient (and suitably musty) basement -- but swappers can't be choosers.

Like the building, swaps are an old tradition. One can imagine women in Victorian England exchanging period clothing and gossiping about the local noblemen. Swaps were once an informal affair, usually held among friends. But now, because of a confluence of factors -- the Internet and social networking, the recession, and the green movement -- they seem to have become a formal and popular trend.

The premise is simple: You drop off clothes and sift through what others brought. No money is exchanged.

I discovered the Brooklyn Clothing Exchange on Meetup.com, where several swap groups in New York are listed. Besides interviewing those who showed up, I also had some clothes to contribute -- gray Levi jeans, 2 vintage T-shirts, a polo shirt, and the kind of long-sleeved Diesel shirt a hip cowboy might wear. I, however, am not a hip cowboy, so it got swapped.

This was the Brooklyn Clothing Exchange’s third swap at the library. Besides the Meetup announcement, its organizers had posted fliers around the neighborhood. I arrived shortly after 1 p.m., passing through the library’s main room, under vaulted white ceilings, and past original oak paneling and dark-brown wooden benches, then down into the basement.

Only a few people had already arrived, and the group’s founder, Kioka Williams, organized men’s, women’s, baby’s, and children’s clothes on long tables along 2 narrow hallways. The selection on the men’s table was sparse.

Williams started the group last November. Most attendees, she said, live in the neighborhood or learned about it via blogs. Williams used to work in the fashion industry in New York and Los Angeles, and she didn't like what she saw -- sheer waste and excess and materialism, she said. “One of my causes is recycling clothing,” she told me. “This is the most feasible way to do it.”