LOS ANGELES — When Kim Kardashian West says it, she’s not being funny. She doesn’t smile. She is professional and sincere, and that sincerity is worth millions of dollars.

Had she made any mistakes when introducing Skims, her line of shapewear, in September?

“I wouldn’t say a ‘mistake,’” she said. Then she listed a few mistakes, concluding with “the pee hole thing.”

“I wish we launched shapewear with a pee hole,” Ms. Kardashian West said. “For the people who don’t want to take it off and on all the time.”

It wasn’t the first time she had brought it up. Five months ago, she talked about it on “The Tonight Show,” during a bit in which she revealed her most recent Google search: “is shapewear with pee hole better.”

“This is so embarrassing,” she said, while Jimmy Fallon giggled and his audience cheered. Ms. Kardashian West gamely grinned, gave an entertaining and half-relatable example of urinating on herself at the Emmys and then seemed to get a little defensive: “No, this is such a legit question.”

Shapewear is compressive; its main function is to make bodies look smaller and feel tighter. It’s supposed to mold limbs to mannequin-like smoothness, paving over cracks, flattening any bloat and restraining all bounce.

It is most commonly sold as high-rise shorts and underwear, though it also takes form as slips, sleeves, leggings and almost anything else short of a full-body skin suit (though there are bodysuits). It usually comes in black, beige or a slightly warmer raw-noodle shade of beige.

For the uninitiated, removing shapewear — to use the bathroom, for example — can be laborious, requiring some yanking and rolling and a base level of forearm strength.

While she only recently monetized her interest in shapewear, Ms. Kardashian West, 39, has been a designer of it all of her adult life. According to personal legend, she was forced to dye, slice and sew her store-bought shapewear for years in order to meet the unique needs of her unique body. Now she is taking on Spanx, an industry giant as synonymous to shapewear as Kleenex is to tissue. Skims, she said, is a modern alternative.

But more important, it’s a comfortable alternative — “really comfortable,” Ms. Kardashian West said. Comfortable enough to wear every day, not just special days. Comfortable enough to want to wear at home, which she does, under sweats. Because Kim Kardashian West, one of the most famous, wealthy and watched women in the world, is at her most comfortable when she’s in shapewear.

For all the products and concepts she has sold to the world over the years, this is the one she is the most confident in peddling: Restraint will bring you comfort.

Weaving $1 Billion

“I am really big on fabrics,” Ms. Kardashian West said. She was sitting on a couch, wearing a plush white robe that was, regrettably, not made by Skims. (Before the holidays, Skims released robes and pajamas made from soft bouclé. Ms. Kardashian West said she wanted to make sleepwear after a “disgusting” realization that she wore only the same three pairs of pajamas, which all had holes in them.)

On its own, the image of Ms. Kardashian West sitting here — right here, on a January afternoon in Hollywood, in the bronzed flesh and not on a screen in someone’s palm — didn’t make any sense. She looked as if she had just taken a shower; her hair was wet, and, along with the robe, she wore chunky white foam house sliders by Yeezy.

But she also had a full face of perfect makeup? Her posture was relaxed, as if she sat cross-legged on this couch every day. But the couch was in a poorly lit conference room, next to a photo studio? As in her “Keeping Up With the Kardashians” confessionals, she rarely emoted while talking. Unless she was talking about fabrics.

“I love, love, love when we do our fittings and fabric meetings,” she said.

The company has a growing inventory — a full line of regular bras and underwear, along with nipple pasties and a mystifyingly flexible hoisting breast tape inspired by gaffer’s tape — but its core product is its shapewear fabric. Made from nylon and spandex or elastane, and formulated depending on the intensity of the shapewear’s squeeze (medium, high or super-high), it took more than two years to develop.

“I knew exactly what I wanted,” Ms. Kardashian West said. “Like the right amount of hold, where it’s not too tight and not too hard to get on.”

Weaving fabrication takes a long time, though, which is why Skims has struggled to restock after consistently selling out of products, Jens Grede, Ms. Kardashian West’s business partner, said in a phone call. Skims operates on a drop model, releasing a batch of new products (or restocking them) every week or so. A drop could have 20,000 units or 200,000 units, the company said.

Mr. Grede, 41, acknowledged that customers are frustrated, but to him the wait is worth it.

“Most great fashion companies are really built on their own fabric base,” he said, referring to Levi’s and Lululemon. “Billion dollar apparel companies are built on identifiable, and not easily replicable, fabrics.”

In November, TMZ reported via “sources with direct knowledge” that Ms. Kardashian West believed Skims would be her billion-dollar company. Her husband, Kanye West, had already built one (Yeezy). So had her little sister Kylie Jenner (Kylie Cosmetics). But Ms. Kardashian West, the family’s original money tree, had not made it there with her pre-Skims businesses, including KKW Beauty and KKW Fragrance.

“I mean, I think everyone would hope to have a billion-dollar business,” she said when asked about the report.

Skims would not provide any financial figures for this article. It would not confirm or deny a separate TMZ article claiming the company made $2 million within its first few minutes, saying only that “sales have exceeded monthly goals and projections.” (It would also not specify where its products are manufactured, though many are tagged with “Made in Turkey” or “Made in China.”)

“I have really high goals and hopes, and I do believe with sales projections, and having amazing retail partners, we will definitely get there,” Ms. Kardashian West said.

The retail-partner aspect of this plan is brand-new. As of Feb. 5, Skims products are available in 25 Nordstrom stores and on the Nordstrom website. (They were previously sold only at skims.com.)

On the day of the release, Skims hosted a pseudo-runway show at Nordstrom in New York. Fans lined the sidewalk for hours before the store opened; the first 50 were promised a photo with Ms. Kardashian West.

Around noon, on the building’s packed fifth floor, bells began bonging irregularly from surround-sound speakers. Dozens of models wearing only shapewear ascended from the escalators and made their way to a podium, where they assembled, joining a few mannequins in frozen poses.

A hundred arms pointed a hundred phones at the assortment, and it truly was an assortment of size, color and age. The women still had visible rolls and cellulite and sagging bits — all the features of a human body that have been marketed as flaws. They weren’t fixed by Skims. They just were

Skims’ move into Nordstrom, though it involves far fewer stores, recalls another young brand moving into bricks-and-mortar: Kylie Cosmetics’ expansion into Ulta in November 2018, a year before Ms. Jenner sold 51 percent of her company to Coty for $600 million.

It took more than two years of trial and error — and occasional website-crashing hype — for Ms. Jenner to get there. Ms. Kardashian West made the move after just five months.

“It was an interesting process to see how a deal like that gets done,” she said of her sister’s Coty sale. “And exciting to see how Kylie built her brand off an insecurity that she had.”

Aside from this veiled sibling rivalry, Skims has ample competition in its own market. A number of shapewear companies with body-positive Instagram accounts have tried seducing young customers in recent years: Honeylove, Heist Studios, Shapermint. But among this group, Skims has the widest size range (XXS to 5X) and color range (nine shades, compared with three or four at the other brands).

The color options are particularly important to Ms. Kardashian West. “I couldn’t find something that would match my skin tone,” she said. “Let alone, how am I going to find something for my girls when they’re older?” (North is 6, and Chicago is 2.)

Spanx, the 20-year-old company that dominates the market, does sell plus-size shapewear, but most items cost $4 more than the same piece in a non-plus size. (“We think that’s horrible,” Mr. Grede said.)

Still, Skims is far from the first of these companies to promise comfort from a garment that is inherently uncomfortable, or to offer an “extra boost of confidence,” as Ms. Kardashian West put it, through compression. But she has a personal sales pitch: her own newfound confidence.

‘Let’s Try it and See’

There’s a scene in a 1999 episode of the VH1 show “Behind the Music” about the band TLC that has stuck with Ms. Kardashian West. It’s a monologue by Lisa Lopes, known as Left Eye, about money:

“This is how a group can sell 10 million records and be broke, and everyone get ready to do your math. O.K., there are 100 points on an album. TLC has seven. Every point is equal to 8 cents. All right, seven times eight is 56 cents. That means every time an album gets sold, TLC gets 56 cents. Sell 10 million records: $5.6 million. Seems like a lot of money. Well, it’s not a lot of money when the record company has spent $3 million to record your album” — and they had to pay back those costs.

She continued: “So, now we have 2.6 million left. Well, guess what? When you have that much money, you’re in about the 47, 48, 49 percent tax bracket, so that immediately gets deducted to $1.3 million. Then you split the rest three ways. You’ve got about $300,000 left, if that. O.K.? $300,000. I can buy a nice house with that. And what am I going to pay my bills with?”

When Ms. Kardashian West explains the “bad deals” she made early in her career, she feels as if she’s doing that monologue.

“Think about it,” she said, offering the example of a 2011 deal with Sears to create a clothing line called Kardashian Kollection. She and her sisters Khloé and Kourtney contractually made 6 percent, which then became 2 percent when split into three. But then they had to give 15 percent of that 2 percent to their agent, plus 10 percent to their momager.

“We’d get, like, almost nothing,” Ms. Kardashian West said, and they’d be “flying from city to city, country to country.” On top of that, she had no real control over the product quality. She didn’t even know she wanted control.

“I credit every business venture that I’ve been in until this point, to really understand what it takes, and how involved you really have to be if you want it to be the best,” she said.

So Ms. Kardashian West has changed, and significantly. But navigating her own power and vision is still a work in progress. Walking into this interview, she was feeling annoyed.

For a few hours she had been shooting a campaign for KKW Beauty, but the results weren’t working for her. She had a very specific concept in mind. The problem was that everyone else in the room had opinions, too.

At one point Ms. Kardashian West had to say: “O.K., I know exactly what I want. So we’re going to do that.”

It’s never like this with Skims; it’s always easy, she said. “It’s really fun for me, and I never get frustrated.” It is “the most confident that I am in any project.”

Before Skims was introduced to the public, people told Ms. Kardashian West that one of her signature products, shapewear shorts with one leg cut off — to wear underneath a dress or skirt with a high leg slit — wouldn’t translate, she said. No one would get it. But she had been cutting off one leg of her shapewear for years.

Ms. Kardashian West said, “Let’s try it and see.”

“It’s a good feeling to really be confident in something, because a lot of the time, sometimes, I’m not,” she said.

There is a catalyst behind Ms. Kardashian West’s growth; it is not just natural career maturation. She didn’t evolve on her own, which may be disappointing to those who have organized her into the #girlboss category of entrepreneurs. It was her husband who changed her, she said.

Mr. West would turn down high-paying opportunities if they didn’t align with his beliefs and goals, and she would watch in awe at his restraint.

“When I first met him, I probably didn’t believe in that or understand that,” she said. “I think I did, at one point, a Carl’s Jr. campaign and a cupcake campaign and a weight loss pill or diet or something, all at the same time. And it was all very contradictory, and my whole mentality has changed now.”

Radical Comfort

Her whole environment has changed, really. Architectural Digest recently published photographs of her family’s cavernous monastery of a home, celebrating its bare rooms washed in white and noting its “uncompromising minimalism.”

The same minimalism permeates Skims’ branding, which Mr. West has guided. The colors are muted nudes; the models are stoic; the photographs, shot by his frequent collaborator Vanessa Beecroft, are soft and rich in their simplicity. The products look very expensive. (They’re on average about $40, reasonable by market standards.)

Skims was not always called Skims. It was announced in June 2019 as Kimono, a name that instantly drew criticism for its appropriation of Japanese culture. But Ms. Kardashian West did not instantly react. She had been through enough internet outrage to know that noise didn’t always last.

So she held back, listened to the concerns and then finally changed the name, which was costly and pushed back the company’s operational time frame.

The name Kimono was first on Ms. Kardashian West’s list of her Skims mistakes, before the whole “pee hole thing.” But it has been a while now, and as Skims is increasingly viewed as a success, not as many people remember the controversy. Ms. Kardashian West has enjoyed a few good months in the press. Right now people want to talk to her about her criminal justice advocacy and efforts to become a lawyer.

She tells them that she has finished the first year of a four-year apprenticeship at a law firm, which in California is an alternative to law school. This summer, she said, she will take the “baby bar” exam, which will determine whether she can move on to her second year. She recently posted a photo on Instagram of a study guide customized for her.

A multiple choice question was posed as a scenario. In summary: A celebrity’s house caught on fire after the celebrity’s boyfriend — who had been lighting up the grill — decided to strike a match on the side of one of Ms. Kardashian West’s beauty line promotional boxes. “Which of the following, if true, would serve as a defense to arson at common law?”

This is the one job Ms. Kardashian West can’t “turn off,” she said. She always needs to study. In bed at night, she watches crime documentaries.

“‘Don’t you just want to watch something else?’” Mr. West has asked her.

“No, I don’t,” she said, laughing. In this arena and in others — makeup, shapewear — Ms. Kardashian West knows what she wants. She says no now, and she never used to say no.

Restraint does have its pitfalls. When a man suddenly materialized during our interview to hand Ms. Kardashian West a large container from Pinkberry (and a plastic cup of sprinkles on the side), she was delighted. When she removed the lid and discovered her frozen yogurt was vanilla and not pineapple sorbet, she was deflated.

“Damn, that’s so annoying,” she said, more to her nearby chief marketing officer than to me. “I’m not going to waste my calories if it’s not perfect.” Texts were sent, and the unseen man — or someone, perhaps another man — was dispatched back to Pinkberry. “If it’s not delish, it’s not worth it.”

Ms. Kardashian West’s diet and body image, like many things in her life, has always been an open book. When she was trying to lose weight after childbirth, she used to post photos of her scale on social media.

Skims’ most recent product drop is her signature waist trainer in a new nude color. (A waist trainer is a corset that “sculpts you perfectly to accentuate your body’s natural curves,” according to Skims, but also “crams all of your organs together,” according to an Atlanta physician.) The Kardashians have long evangelized waist trainers, wearing them at the gym or, especially, while relaxing at home.

This is how Ms. Kardashian West will get to a billion dollars, if she does indeed get to a billion dollars: by convincing people of the radical idea that shapewear is casualwear and loungewear, too, when its domain has previously been first dates and party outfits. The logic used to be that shapewear was like armor — supportive protection for moments when you may feel exposed. But now everyone is exposed, all the time.

Ms. Kardashian West said it makes her happy to FaceTime with her sisters when they’re at home and to see they’re wearing Skims, “you know, not for a photo,” she said. “It’s genuinely the most comfortable thing for them.”

“I feel better when I’m wearing shapewear,” she said. “That’s just me.”