Laura and Kate Mulleavy stand side by side in front of a dress form, 32-23-34, propped on a metal chair so that it seems nearly 6 feet tall. The form wears a half-completed gown for their fall 2007 collection. At the moment, it looks like a chiffon sheath with a seam across the bust and a row of knife pleats at the calf.

Laura begins to pin long strips of pinked-edge chiffon, organza and heavy-weave gauze along the neckline. She exhales heavily and seems slightly exasperated as she pins and re-pins. Each strip is placed one inch from the next, and they hang in loose columns from neckline to hem. The effect is precarious: Even a hint of circulating air causes the pastel fabrics to shiver and wave.

"For me, that's really pretty," Laura says as she holds up the next strip, a rose chiffon. "You don't think it's too candy-stripey?" Kate asks. "Well, if it doesn't work for you . . . "

Laura holds up a blush-pink organza, then the gauze, then another shade of chiffon. Finally she tries a paler color, a strip of ivory.

They stare at the strip of ivory for a long time.

"I think the happy accident works better," Kate concludes. Laura continues pinning.

"People don't realize how long it takes to make a dress," Kate says.

It takes a long time for these two. The Mulleavy sisters' attention to detail has been described by critics as "couture-like," "obsessive" and even "relentless." A Rodarte gown might incorporate 100 pleats, hand-sewn roses in 25 fabrics, burnt ostrich and pheasant feathers, and thousands of Swarovski or antique crystals from the Czech Republic. Frothy tiers of organza might be layered over what looks like a chain-mail tunic made of beaded lace, and a sihouette might swell into poufs at the bust and hips. These are otherworldly creations in the flimsiest materials, suitable for mermaids or nymphs—and very few women.

On a Saturday morning, the twentysomething sisters are sewing in their skylighted studio not far from Staples Center. Their father has just left after dropping off some suitcases he didn't want them to store in the house anymore—the girls still live with their parents in Pasadena, and seem to keep their loved ones close. Sitting among the handmade flowers, piles of pleated fabric, stuffed lions, a black lacquer male bust and stacks of fat coffee-table books on geishas, turn-of-the-century toys, fashion, dance and art history, they describe their idyllic upbringing.

"It really affected us, all those magical places where we grew up," Kate says. Their most important memories are of a one-story house in Aptos, an academic town near UC Santa Cruz where making money was "almost looked down upon," not far from the famed monarch groves of Capitola. Their father was a botanist specializing in fungi; their mother painted and wove Navajo-style wall hangings. The girls were encouraged to explore, and when their grandfather (a World War II veteran) would visit, he'd take them marching through the mustard fields and apple orchards at dawn. The sisters start giggling. "We thought it was fun, but when you're little you don't really realize that you're . . . well, marching," Laura says.

When the girls were teenagers, the family relocated to a house on their grandmother's property in Pasadena. The new locale offered a different kind of visual stimuli. "It's amazing," Kate says of the architecture in the area. "You have '60s modern, Craftsman, cottage homes, the Gamble House, Frank Lloyd Wright, crazy stuff like French Tudor, English Tudor and French country houses all next to each other—and bungalows." They also haunted the Huntington Botanical Gardens and the Rose Tree Cottage tea shop. After attending UC Berkeley, where Kate studied art history and Laura English lit, they returned to the same house.

As they talk about their influences, they sound alternately brainy and childlike. They're fans of the great American couturier Charles James and French icon Coco Chanel, Audrey Hepburn and Wong Kar-Wai movies, and costume designers Adrian and Karinska. They read books on antique toys and visit the children's section at the main branch of the Pasadena Public Library for its "warm room" and comfy pea-green chairs. They've always felt a deep connection with their surroundings, and Kate elaborates on their California roots. "[It's] one of the major influences that we have, growing up in that natural landscape," she says. "I talk to other people who grew up in that area, and like anyone who does stuff on a visual level, they have this weird obsession with shadow and light, and how can we emulate certain natural forms."

Their first collection, for spring 2006, included gowns such as Look #15, which might have been inspired by starfish or stingray eggs, with long black points dripping down the pleated georgette front. Their second collection, for fall 2006, drew even more directly from the natural world: Folded organza formed appliqué leaves and branches; rippling waves of georgette, chiffon and organza whispered as the models walked down the runway; one silk-and-wool suit had a neckline resembling the curved inner petals of a flower; another was made of cashmere and chiffon panels that looked like scales. Their spring 2007 collection, inspired by the 18th century portrait painter Thomas Gainsborough, photographer Richard Avedon and the Huntington Gardens, explored volume, with dresses unfurling and blooming into fecund shapes. The fall 2007 collection continues the verdant theme, but also introduces heavier fabrics, such as brocade, and architectural constructions.

Most of their fabric is pinked—"that's our signature," Kate says. The chiffon strips Laura has been pinning and re-pinning are another signature, which began as an attempt to re-create the rough bark found in a redwood forest. Now Kate piles layers of kidney-shaped pieces of black lace and gold lamé across a lace blouse to form a three-dimensional soft collar. On an industrial kitchen table behind her, there are piles of pink hand-sewn roses of organza and chiffon. They look like mitochondria or a microscopic membrane: waving, folding and tucking under one another as if they have no beginning and no end.

Christine Suppes, publisher and editor in chief of the website Fashion Lines, is one of a handful of women in the world who buy couture, and one of the slightly larger handful who wear Rodarte. When she was in Paris for the couture shows in January, she stopped by Colette, a boutique known for showcasing avant-garde designers. "People were crowded around the Rodarte dresses, putting their hands all over them trying to figure out how they were made," she says.

The intricacy of the Mulleavys' creations has attracted massive amounts of attention. Cameron Silver, owner of the vintage store Decades in Los Angeles, Vogue European editor at large Hamish Bowles, who has a large couture collection, and most recently Valerie Steele, director of the Fashion Institute of Technology Museum, have all shown intense interest. Silver introduced the sisters to Vogue editor Anna Wintour, and the rest is hype history. They made the cover of WWD their first season and have been profiled in all the go-to fashion magazines: Vogue, Paris Vogue, W. Meanwhile, Bowles ventured to their Pasadena home with shoe god Christian Louboutin for lemonade, and Steele has asked for several of their pieces to add to FIT's permanent collection.

As the sisters continued to show, however, the critical accolades peaked. Although most of the fall 2007 collections shown in New York last month explored sleek silhouettes, sharp lines and space-age shapes, the Mulleavy sisters were still focusing on natural imperfections, fractals, unfinished edges. The critics seemed impatient, suggesting that the designers were working in a state of "panic" or "fatigue," and musing on when their clothes would go "from palatable to acceptable."

The designers themselves say they welcomed the criticism. "If you don't strike passion in someone, good or bad, then you are not doing the right thing," Laura says. "I think that the worst thing I saw was someone who said that we made 'a pretty chiffon dress.' That hurt my feelings."

Susan Foslien, who sells Rodarte at her two Susan's stores in Burlingame and San Francisco, blames the early hype. "These two people aren't from the industry, they have great imaginations, I think they are still raw and I think they are still collectible." She also blames the way Americans shop. "Everything on a hanger has to look great in America. They take seven minutes to shop, and they don't understand the construction." She sells Rodarte pieces to those who appreciate the craftsmanship. "If you match clothing to a client, it's a great marriage," she says. "It's the same with an artist and a collector."