Monica Zwirner and Lucy Wallace Eustice, the founders of MZ Wallace, were in their offices on Crosby Street in SoHo recently. On the table in front of them lay fabric swatches and samples for an upcoming collection. But the pair had turned their attention to a look book they had produced over a decade ago.

“I’m scared to look,” Ms. Zwirner, 60, said. “This is so old.”

Ms. Wallace Eustice, 57, opened to a photograph of a shoulder bag. “That’s good,” she said cautiously. She turned the page to look at another picture of a purse. “And that’s …fine.”

“That’s not bad,” Ms. Zwirner admitted. She quickly flipped through the rest. Ms. Zwirner seemed relieved. “This actually feels good — to revisit something you made so long ago and realize it still looks OK.”

MZ Wallace — the moniker is a combination of Ms. Zwirner’s initials and Ms. Wallace Eustice’s maiden name — is a 22-year-old handbag and accessories line that makes utilitarian, no-nonsense shoulder bags, totes, duffels, backpacks and other carryalls out of sustainable nylon fabrics.

The brand is not a household name. It does not possess a bold, easily identifiable logo or color scheme like Chanel’s interlocking C’s or the Gucci stripe. It does not advertise in fashion magazines. It has avoided famous endorsements and flashy marketing campaigns.

But it has nonetheless achieved a cult status among stylish urbanites and a long list of celebrities that include Jane Fonda, Jennifer Garner, Anne Hathaway, Blake Lively, Sienna Miller, Julianne Moore, Lupita Nyong’o, Sarah Jessica Parker, Reese Witherspoon and Renée Zellweger.

This past August, MZ Wallace opened a new flagship store, just across from their offices on Crosby Street, designed by the architecture-and-design firm Charlap Hyman & Herrero. The 1,900-square-foot space is blanketed with carpets, curtains and wallpaper decorated in an oversized trompe l’oeil marble print, inspired by Gio Ponti’s marbled rubber floors in the Pirelli Tower in Milan.

Its southernmost wall is hung with artwork by Wolfgang Tillmans and Christopher Williams. Metallic pedestals by the artist Shun Kinoshita dot the display floor alongside beige-colored Mario Bellini chairs. A second store in Chicago — where the brand has a similarly strong customer base — opened at the same time.

Call it a high-low vibe. The brand owes its longevity and success to its clever ability to marry practical design with luxury details. MZ Wallace’s most popular style of fabric, a quilted puff nylon, serves as a discreet brand emblem, as does a small diamond made of Italian leather sewn on each product’s bottom gusset.

The proportions of each bag are intuitively functional: a large, roomy tote slides perfectly on top of a carry-on suitcase; a slender cross-body bag can comfortably fit your wallet, passport, keys and phone. Certain features reveal a thoughtful functionalism, such as the clips on an 18-pocket backpack that allow it to fasten to a stroller.

Their bags also come with Italian leather trimmings and silver hardware. Some are decorated with a bit of playful fringe, a fashionable chain or pretty leather-wrapped straps. And while black is an ever-popular customer color choice, each season a new collection arrives in a variety of bright, bold hues and patterns — a peony pink here, a muted sapphire blue there — all at relatively reasonable prices. While not inexpensive, a weekend duffel bag, for example, retails for $295; a shoulder bag for $185. (By comparision, a designer handbag today can start at around $1,500.)

“Not that we have anything against expensive bags,” Ms. Wallace Eustice said. “MZ Wallace is either your first bag or your second bag. Some women like to have a more traditional designer bag and just use us as their traveling tote or weekend bag.”

“We wanted to create bags that help you be — it sounds a bit cheesy — a better you,” Ms. Zwirner added. “The bag’s not wearing you. And it can help you get through your day, whatever kind of day you’re having and whatever type of person you are.”

“I remember coming to the conclusion that they were, in a way, the American answer to Longchamp,” said Adam Charlap Hyman, 32, the co-founder of the design firm Charlap Hyman & Herrero. “They were rendering something that feels elegant in a material that is very practical. They’re not trying to be something they’re not.”

Ms. Zwirner first began contemplating starting a handbag company when she was a young mother in the late ’90s. As a former fashion stylist for Barbara Dente and an interior designer for Selldorf Architects, she loved Prada’s nylon bags, but found them too expensive. Kate Spade had launched her line of popular nylon box bags in 1993, but Ms. Zwirner found its aesthetic was too girly, and more traditional brands like LeSportSac and Hervé Chapelier had been around since the ’70s, leaving room for innovation.

“I remember thinking that there wasn’t a great American nylon handbag company that was focused on style and design in a way that appealed to me,” Ms. Zwirner said. “But I also knew I couldn’t do it alone. I had three small children and building something by myself just wasn’t possible.”

When Ms. Zwirner ran into her friend, Ms. Wallace Eustice, at New York’s Union Square farmer’s market in the spring of 1999 — she with her youngest in a stroller; Ms. Wallace Eustice with her newborn in a carrier — Ms. Zwirner asked if she was interested in discussing an idea.

Ms. Wallace Eustice — a former accessories director who had worked at Mirabella, Harper’s Bazaar and Elle — immediately liked the concept. But, she added, they would need a store. She had gotten her start in retail with the shoe designer Manolo Blahnik and had witnessed firsthand how much of its success had depended on a brick-and-mortar presence. With a store, they could have relationships with their customers, which would be crucial in knowing what to sell. They wouldn’t be beholden to the whims of a department store.

“It was direct-to-consumer before there was DTC,” Ms. Wallace Eustice said, referring to today’s online practice of selling to the customer without a middleman.

MZ Wallace debuted in May 2000 on Crosby Street, just a block north of their current flagship. They sourced their nylon from Brookwood, a textile company known for making high-tech military and medical fabrics. To achieve their coveted quilted effect, they ran bolts of nylon through mattress quilting machines in Brooklyn, which they then delivered to Manhattan’s garment district to be manufactured.

Initially, they offered a tote, a satchel and a shoulder bag. Word of mouth quickly generated interest, as did press from Ms. Wallace Eustice’s friends and colleagues at various fashion magazines. But their bags were also, Ms. Zwirner said, popular with a “a local customer — downtown moms who heard about us, playground discoveries.” Soon, they had gained an avid following with Japanese customers. “At the time, we were bigger in Japan than here,” Ms. Wallace Eustice said.

“By the way, they really only sold three bags,” said the fashion designer Isaac Mizrahi, 61, who was an early customer. “I promise you that. You couldn’t get more. There were three styles. That was it. Bye-bye! And they were great and everybody wanted them and they couldn’t keep up with it.”

As Ms. Wallace Eustice predicted, early buyers at department stores didn’t understand the brand. They were told to change and raise their prices. But the two stuck to their vision. They never altered the simplicity and practicality of their designs to be like the trendier bags of the early 2000s such as Botkier, Kooba and Rafe that have now passed out of fashion.

“Accessories often change to fit the needs of the consumer as times change,” wrote Debbi Hartley-Triesch, 54, the executive vice-president and general merchandise manager of Beauty, Accessories, and Home at Nordstrom, the luxury department store that has carried MZ Wallace for over a decade, in an email. “Bags are often an extension of ourselves, both in self-identity and utility.”

As MZ Wallace grew, so did its sense of purpose. Ms. Zwirner is married to the German art dealer and gallerist David Zwirner, and in 2011, she and Ms. Wallace Eustice launched a special-edition bag, designed by the artist Raymond Pettibon, to raise money for Artists For Haiti, a non-profit organization founded by Mr. Zwirner and the actor Ben Stiller. Since then, they have produced special-edition bags with artists and organizations such as Kerry James Marshall, Njideka Akunyili Crosby, Glenn Ligon and others — with 100 percent of proceeds donated to a chosen non-profit organization.

“I love to carry my Glenn Ligon bag because it often prompts conversations about what’s most important to me, which is art and artists,” said Thelma Golden, 57, the director of the Studio Museum in Harlem, for which MZ Wallace raised close to $100,000 with Mr. Ligon in 2014 for its art education programs. “It gives me the chance to be the museum curator I am.”

“To me, the bag is the canvas,” said the artist Nick Cave, 64, who most recently designed a colorful MZ Wallace tote where all proceeds went to support educational programs at the Museum of Contemporary Art Chicago and Facility Foundation. “It’s this extension of an art practice. And I love the idea that it is out in the world, being seen and being recognized.”

Today, MZ Wallace employs 40 people and offers over 400 different styles. Much of its manufacturing is now done in China and Vietnam. 60 percent of their sales occur online, from their website, which launched in 2004. Ms. Zwirner and Ms. Wallace Eustice said in the last three years the brand has grown by 20 percent and, excluding the year they opened, have only seen year-over year growth.

Ms. Eustice and Ms. Zwirner have been approached on several occasions about selling their company, which is still privately held. They are open to the idea. But they also like where they are. The two have lunch every day at the office. They remain close friends. “We have a laugh,” said Ms. Wallace Eustice. “You have to have fun along the way. Otherwise, what’s the point?”