The world’s first fully compostable swim suit will debut at a Swim Week runway show featuring designers who specialize in “sustainable” fashions that eschew man-made materials like polyester.

Swim Week on South Beach is mostly about glitz, glamor and impossibly leggy models traipsing about celebrity-lined runways.

But at one Friday night show at The Setai, it’s also about trying to save the planet — one itty-bitty bikini at a time.

A group of “eco-couture’’ designers will unveil lines that eschew synthetic textiles like polyester. Instead, they’re crafting “sustainable” swimwear out of fabrics made from wood pulp, hemp and bamboo or from recycled plastic bottles, “upcycled’’ factory scraps of cotton and nylon and “repurposed’’ material like military parachutes.

Designer Linda Loudermilk said Thursday that she would debut what she billed as the world’s first fully compostable bathing suit.

It’s fashioned from a plant starch, she said, that has been turned into a fabric so new she just got her hands on it four days earlier. She said the suit won’t dissolve on a woman’s body, but bury it under dirt, like in a land fill, and it would break down within 180 days — leaving not a single spandex strap, blot of chemical dye or foam bra cup insert behind.

“You can use it again or you can throw it away,’’ said Loudermilk, a pioneer of the eco-fashion movement. “It’s very inexpensive so it’s something you can give to your guests but it has a fashion forward look.

The show, dubbed “Haute Natured,’’ will feature Loudermilk’s “Luxury Eco’’ line as well as environmentally friendly designs from Eco Swim by Aqua Green, Meadow and MAE Couture.

Alas, another cutting-edge piece of apparrel, the solar-powered bikini, will not make it to Miami, owing to a travel issue for the designer, said show producer Ryan Hattaway. Covered with flexible photo-voltaic strips, it is billed as being capable of recharging small devices yet is fully submersible — at least once the cell phone is unplugged.

Eco-couture has been around for years but it’s relatively new for women’s swim wear, typically constructed of man-made materials specifically designed to dry quickly or hold shape. That often means they contain chemicals and are nearly impervious to the forces of a compost heap. Polyester is actually made from the same stuff as many plastic bottles, polyethylene terephthalate.

Using sustainable materials poses a lot of challenges, said Jenni Saylor, the designer for Eco Swim By Aqua Green. In fact, she thinks it’s impossible to make a suit that will appeal to women without at least a little spandex, AKA lycra, which is the stuff that makes a suit cling in the right places.

“If it doesn’t look good, they’re not going to buy it just because it’s sustainable material,’’ Saylor said.

“Eco-cell’’ foam bra cups, made with biodegradable plant oil, are one of Eco Swim’s big features. The suits are made from recycled nylon, polyester and cotton. Saylor stressed fabric isn’t picked from old clothes bins but comes fully processed and cleaned from manufacturers.

“It’s absolutely not recycled clothes,’’ she said. “A woman would be totally disgusted by that, especially when it’s touching your body that close. No, no, no.’’

The designers extend the eco theme beyond the suits. Eco Swim’s packaging and labels are all recycled materials. On her beach wraps, Loudermilk, based in the Hollywood on the West Coast, has printed environmental images such as California wild fires.

Given that by definition they doesn’t amount to much material, biodegradable bikinis aren’t going to make a big dent in the waste stream. But the designers believe wider adoption of the innovations could have real impact. Saylor said the company is considering sharing its techniques.

“It’s not about us,’’ she said. “It’s about the environment.’’

Both designers said eco-couture reflects a lifestyle choice and should appeal to women who, for instance, buy organic food and products. Loudermilk said it’s an ethic that emphasizes health and balanced, sustainable living, not a return to the hippie era, when the clunky Birkenstock sandal defined environmental fashion.

“This is the new meaning of luxury,’’ said Loudermilk. “How many Gucci glasses and Louis Vuitton bags and products can you have? The luxury eco movement is giving people a way to be proud of what they’re choosing to wear.’’

Ticket prices for the show start at $50. The event begins at 9 p.m., with the runway show starting at 10 p.m. Proceeds will benefit The International SeaKeepers Society. For information: www.hautenatured.com.

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