Rosie Assoulin presented her Spring 2015 collection in New York City at Notre Dame School during Mercedes-Benz Fashion Week in September. (Taylor Hill/Getty Images)

The womenswear designer Rosie Assoulin is rooting around under one of the numerous layers of a floor-length skirt worn by a resolutely unflappable young model. In the middle of the Catholic school gymnasium that is serving as her temporary showroom, Assoulin is trying not to cause a stir by crawling around on her hands and knees in front of the crowd of editors who have assembled to inspect her Spring 2015 collection and to ask her to wax poetic about her inspiration.

But there’s a point she needs to make. The chief executive of her company — her husband, Max — is called upon to discreetly lend a hand. He locates a tiny zipper tag, gives a tug . . . and the lower portion of the skirt spirals free, detached from its top two-thirds. The skirt now ends at the knee — a more versatile garment.

Assoulin loves clothes that make sense. One might assume that this would be the case with any designer, but in fact, it is rare. Just as sports cars deliver more bragging rights and cornering thrills than sensible gas mileage, most designer clothes offer dazzling lines and delicate hand-tooling but no place to tuck a lipstick and house keys.

So for women who have puzzled, for example, over the near-pathological lack of pockets in evening wear, Assoulin hears you. And she has come through.

“Evening wear — it just needs to work, man,” she says. “I need a place to put my hands.”

Assoulin “respects the woman she’s dressing,” observes friend and fellow designer Brian Reyes. Her clothes are pragmatic. A word that Assoulin especially likes.

Not that Assoulin is inclined to sacrifice style or creativity for bland practicality. She won’t climb atop a soapbox to rail against the tyranny of mummifying skirts, for instance. “I’ll see a hobbling skirt on a girl in the street, and she’s pulling it off,” Assoulin says with awe and admiration.

She loves fashion too much to hate its frequent streaks of illogic. “I don’t want to use the word ‘exploitative.’ It’s not what it is,” she says of her industry. “It [should be] about the woman . . . but there are so many types of women.” And, apparently, there are a few who appreciate a skirt that makes walking a challenge.

Designer Rosie Assoulin lives in New York. Her entire collection is made in America, most of it in New York’s Garment District. She says it’s reassuring to know she can hop on the subway from her downtown studio and arrive within minutes at the center of her production. (Jesse Dittmar/For The Washington Post)

Assoulin’s business is in its second year. At 29, she has found her voice with astonishing speed. She is a bold colorist with the instincts of a sculptor whose point of view comes through most eloquently in her evening wear.

She is influenced by mentors — designers with whom she interned, the late Oscar de la Renta and the Paris-based Alber Elbaz — who demonstrated an unwavering belief that clothes should be a pleasure, not a challenge. And Assoulin’s work has the potential to speak to women of many ages the way de la Renta’s did, her polished grace helping to fill the expansive void that his death leaves.

She will present her Fall 2015 collection in the thick of New York’s Fashion Week, which begins Thursday. Once again, it will be an informal presentation rather than an elaborate, expensive runway show. For fall, she’ll introduce prints into the collection, but there is no overarching inspiration aside from her own interest in line and cut. Each piece is meant to stand on its own.

Assoulin is the rare woman generating buzz among a generation of designers dominated by boy wonders. “It’s interesting when women design for other women,” says Carrie Kane, co-owner of Chalk, a boutique in Evanston, Ill., that sells Assoulin’s collection. “The designs are very thoughtful and beautiful, but wearable.”

To be fair, many male designers are simpatico with the workings of the female mind, too. Still, there is something real about the woman-to-woman connection.

[New York Fashion Week: Will menswear outshine womenswear?]

“I love the way women design,” says Reyes, pointing to brands such as The Row and Céline. “It’s about comfort, ease and structure.”

But an affinity for practicality can turn into an assumption, and then, a burden. Female editors and retailers seem more willing to be swayed by a young Pygmalion rhapsodizing about some fanciful but unflattering silhouette than a young woman doing the same.

Women can be pigeonholed as reasonable and logical designers, while overlooked as inventive ones. Indeed, when Opening Ceremony’s Humberto Leon and Carol Lim presented their collection as a cheeky one-act play, writers Spike Jonze and Jonah Hill portrayed Leon as the free-thinking artist and Lim as the all-business tyrant.

Assoulin “gives women a reason to dream,” Reyes says, while still making clothes that are “extremely wearable.”

Floor-length skirt and camisole from Assoulin’s Spring 2015 collection. (Sophy Holland)

Fancy trousers — with pockets — from Assoulin’s Spring 2015 collection. (Sophy Holland)

Assoulin has become known for her evening apparel in part because it is not frilly, overtly sexy or tied to vintage glamour. She has found a fourth way: sophisticated and feminine, sculptural but not awkwardly so. Her evening wear, as well as her daytime clothes, possess a decorum that speaks broadly to the modern era — without reveling in disheveled chic.

“If someone gets dressed up in the middle of the day, we look at them weird. I’m not trying to change it but address my own place in that.” So Assoulin says she asks herself, “How do we make [sportswear] feel elevated somehow, but you can still get down and dirty?” She would like her clothes to serve as a serene revolt — a stroke of red lipstick worn in “rebellion of the yoga pant.”

She wants her clothes to be “special but not precious.”

“You never want something in your closet that feels too precious to wear.”

Assoulin, tall with deep-set eyes and dark hair, lives in a low-rise Tribeca building where, like a movie scene of fantasy Manhattan, the elevator opens directly into a white, brick-walled loft she shares with her husband and two children. The sitting area is a field of neutral textures — Mongolian lamb rug, gray sparkly backrests, shaggy pillows — punctuated by a couple of Maarten Baas smoke chairs.

She grew up in Brooklyn and went to a conservative Yeshiva school, a fact she stage-whispers. It was not as cloistered an environment as one might assume, she assures: “It’s New York City. It’s all a fashion show.”

Her parents worked in manufacturing and licensing for childrenswear. Her great-great-grandparents were in the handkerchief business. From the beginning, Assoulin had a window onto the nonglamorous reality of the fashion world.

“I look back at that — making and selling handkerchiefs. It’s like making the sausage and eating the sausage. You never want to see the sausage being made.”

Always creative, Assoulin enrolled at the Fashion Institute of Technology but, after four months, realized the academic route wasn’t for her. An early mentor came from the glossier side of the business: Roxanne Assoulin — mother of the childhood friend who would become her husband — designed runway jewelry for de la Renta. That connection got her an interview, and she was hired as an intern for de la Renta.

“You get sandwiches — a lot of sandwiches. You Xerox a lot. You organize pens. You move around with a lot of black-and-white garment bags that you have no idea what’s inside of. But you’re close and in the thick of everything,” she says. “The fittings, I learned the most from. There’s a picture from Women’s Wear Daily from ten years ago, and I’m in there with Mr. de la Renta holding the pins.”

She spent almost two years in the rare New York atelier where an idea moved from sketch to muslin to garment under one roof. “Even if you see the toil and the sweat, it’s magical. You see these bolts of couture fabrics, ruffles being hand-sewn and embroidery spilling out all over the room,” Assoulin recalls. “You can’t get it out of your head.”

She marvels at the length of de la Renta’s career, which spanned about 50 years. “You look at fashion, and sometimes your work is on trend. Sometimes it’s not. If you’re in it long enough, you see it circle back. For him, it wasn’t always about [magazine] editorials and [crowded] fashion shows,” Assoulin says. “But he was loyal to [his] women.”

After de la Renta, Assoulin worked informally with Reyes, whom she met at de la Renta, as he launched his own brand. Soon, however, she moved to Paris to work at Lanvin, where Elbaz was creative director.

Her time at de la Renta comes through most strongly in her collection. It is gracious, specific and aimed at longevity.

Some pieces in Assoulin’s Spring 2015 collection included interesting back details. She showed the collection in New York in September. (Taylor Hill/Getty Images)

Assoulin’s clothes are expensive. Very expensive. A hand-knit sweater is $1,800, a maxi skirt is almost $3,000. The collection has struck a chord with big-spending philanthropists, well-to-do professionals and customers in the Middle East, says Chalk co-owner Sharon Watrous.

The hefty cost belies Assoulin’s desire to create clothes that aren’t too precious to wear. Few women would throw on such pricey frocks just for a trip to the market. But Assoulin, on an afternoon at home, easily wears a pair of her roomy chocolate-brown trousers with a black turtleneck.

Her entire collection is made in America, most of it in this city’s Garment District, which is a boon for less established designers. “If there was no Garment District here, there’s no way this would be happening,” Assoulin says. “It would be too scary.” It’s reassuring to know she can hop on the subway from her downtown studio and arrive within minutes at the center of her production.

For spring, she showed 32 looks, a small collection, which adds to the cost of her clothes. She is using high-end fabrics such as silk faille. For fall, she designed her own prints.

Retailers acknowledge that the clothes are luxurious in construction. But Assoulin assigns a more emotional definition to the notion of luxury. “For me, it’s about having a special need met, being heard and understood. It’s about being able to go find just the right thing for you.

“To find self-expression,” she says. And an evening gown with pockets.