Shiyue Jiang of George Washington University tries on a cap and gown made from recycled materials. (Nikki Kahn/THE WASHINGTON POST)

When George Washington University’s Class of 2012 marched across the Mall to accept its degrees Sunday morning, the nation’s back yard was transformed into an eco-fashion runway.

Sure, the men wore dress shirts and slacks while the women donned colorful spring dresses and shoes that wouldn’t sink in soft soil. But on top of these outfits, each GWU student sported the newest trend: gowns made from plastic bottles.

More than 5,000 graduates at GWU joined hundreds of thousands of other students across the country in forgoing traditional polyester gowns for versions made entirely from bits of melted plastic.

“The ‘green’ gowns look and feel the same, and the students were really excited,” said Robert Blake, the manager of the GWU bookstore and a member of the university’s regalia committee. “For us, this was really a no-brainer.”

The eco-friendly fashion statement is part of a larger effort by colleges and universities to reduce the carbon footprint of commencement ceremonies. With paper graduation announcements and diplomas, and plastic cutlery and tableware for non-sustainably grown meals and snacks, graduation day has been an eco-warrior’s nightmare.

That began to change several years ago. Unity College in Maine, for instance, sends online invitations, while Pace University in New York prints programs on recycled paper with soy ink. Boston University uses compostable tableware. New York’s New School decorates with local, seasonal flowers. Southwestern University in Texas serves organic refreshments. College of the Atlantic in Maine, which has never used caps or gowns, has had zero-waste graduations since 2005.

And then there are GWU’s plasti-gowns, each spun from 29 post-consumer bottles. In all, about 145,000 bottles that might otherwise have ended up in landfills hung from the shoulders of the graduates.

In addition to GWU, several other nearby schools, including Catholic University, Johns Hopkins University and the University of Maryland, used graduation gowns made of plastic bottles (with such names as “Repreve” and “GreenWeaver”). Georgetown University’s “Elements” line of gowns is made of tree fibers and certified by the Department of Agriculture as a “bio-based” product.

Herff Jones, the company that sells GWU’s gowns, reported that 140 U.S. schools placed orders for the gowns this year. Virginia-based Oak Hall Cap & Gown reported orders from more than 100 schools.

It is important to note that these gowns are nothing like the clingy, colorful, plastic ponchos donned by weathermen reporting from the eye of a hurricane. (You know that’s what you’re picturing.)

The “green” gowns look and feel just like the ones worn by previous generations because — fun fact — the gowns of yore were made from the same material that is used to make plastic soda and water bottles. But instead of using virgin polyester, the gowns are made from bottles that have been crushed or melted down into pellets and then spun into polyester yarn. The yarn is knit into fabric, dyed and sewn into any type of clothing, from graduation garb to ball gowns.

In most instances, according to manufacturers, the recycled gowns cost slightly more to produce, but they sell for nearly the same price — only $1 to $2 more — as the standard ones. GWU undergrads paid $42.95 for the gown, or $51.50 for cap and gown.

“There are a few more costs associated with it, but not enough to make us want to raise our prices,” said Tom Carew, a vice president at Herff Jones who oversees the company’s cap and gown division. “We’re just glad to be able to maintain our commitment to doing good in the world.”

Over the next 18 months, Carew said, Herff Jones expects to develop a recycled-materials fabric that can withstand dry cleaning and multiple wears as part of its rental program. Until then, the company will collect recycled gowns after graduation, break them down and re-recycle them into new gowns.

Recycling bottles into fabric began in 1993, when the outdoor clothing manufacturer Patagonia introduced fleece products made of post-consumer bottles. Now, such companies as Hanes and UnderArmour make athletic garments out of plastic bottles. For the 2010 World Cup, some teams — including the U.S. soccer squad — wore Nike uniforms made from recycled bottles.

Stores ranging from the hip Brooklyn Industries in New York to the high-end Fred Segal in Los Angeles have sold plastic-based T-shirts coveted as much for their softness as their eco-cache.

Even couture designers have sipped on the “green” Kool-Aid: At this year’s Oscars, Livia Firth, actor Colin Firth’s wife, wore a Valentino gown made of polyester produced from plastic bottles. But for GWU and other universities, the recycled gowns go beyond making a fashion statement.

“Using recycled gowns really fits into the ethos here,” which includes student groups dedicated to sustainability, a campus garden maintained by students and a new minor in sustainability, said Sophie Waskow of GWU’s Office of Sustainability.

“This a really great time to be greening our campus, and we hope our students will carry on this commitment after they leave GW.”