Sliding into shapewear for the first time feels a little like vacuum sealing oneself.

As someone who’d never worn the stuff before, it was, at best, noticeably uncomfortable. At worst, my internal organs felt so squished that I raced to the bathroom to shimmy out of it halfway through the work day.

My ill-fated experiment was an attempt to understand how a garment designed to remold the body could simultaneously be described as empowering and anti-feminist, depending on whom you asked.

Though the body-positivity movement and self-love preaching stars like Lizzo are more popular than ever, and many women are ditching their underwire bras for more comfortable alternatives, shapewear has maintained a viselike grip on America’s midsections. Nearly 20 years after Oprah named Spanx a “Favorite Thing,” that grasp shows no sign of loosening.

Celebrities broadcast wearing it on the red carpet to signal their relatability. Shapewear ads featuring women of various sizes wiggling into the garments flood social feeds. The language has evolved, too: In September, Kim Kardashian West debuted her line of “solutionwear,” perhaps unwittingly framing women’s bodies as a problem.

Sales in the United States shapewear market were valued at $526 million for the year ending in August, according to the NPD Group, the market research firm. The surge in online businesses peddling shapewear and advances in product innovation have created a shift in the industry over the last year and a half, said Marshal Cohen, NPD’s chief retail analyst.

“It isn’t just your grandmother’s girdle anymore and it isn’t your mother’s unitard shapewear,” Mr. Cohen said. It targets specific areas, like buttocks or belly. It’s easier to slip on or off (as it’s no longer reserved for special occasions). And, in some cases, it’s made to be seen.

New companies, some direct-to-consumer, check all the boxes of millennial marketing: pale pastel colors, sans serif fonts, ethnically diverse women with a range of body types and robust social-media campaigns. Their message is one of inclusion and empowerment, even (perhaps paradoxically) emancipation.

As Toby Darbyshire, the male C.E.O. of Heist Studios, an online tights and shapewear company headquartered in London, put it, “We want to build the most liberating underwear brand in the world.”

It’s a Cinch

People who work in the shapewear industry tend to have the same talking points, many derived from Spanx’s own oft-repeated origin story.

They will bring up the “Bridget Jones moment,” the one where Renée Zellweger’s character famously dons an enormous pair of figure-smoothening granny panties. They’ll likely tell you that shapewear, like jewelry, or makeup, should be a choice. They’ll say that they aren’t forcing you to wear it, or stating you need it to look good — they’re simply offering it for the people who seek it. (In a written statement, Spanx said that the company’s mission “has always been — and always will be — to help women of all shapes and sizes look and feel their best,” and suggested that Spanx helps “empower” women with its products and philanthropy.)

To a generation that would cringe at traditional, sexist marketing like “nothing beats a great pair of L’eggs” and throw Spanx’s paper catalogs right into the recycling, new companies are taking a take-it-or-leave-it approach. Shapermint, a popular online shapewear marketplace that sells lines by its parent company, Trafilea, alongside other brands, advises visitors to its website to be confident “with or without shapewear.”

Stephanie Biscomb, Shapermint’s brand manager, said that shapewear isn’t about hiding the body. “It’s underwear, it’s not miracles,” she said. “In my case, and a lot of women’s cases, it’s about wearing something that makes you forget how your clothes are fitting.”

While the site has a large customer base over 45, Shapermint’s audience is also getting younger, according to Ms. Biscomb, and the company estimated that about half of the site’s customers are first-time shapewear buyers. The styles that tend to resonate with younger customers are the products with less compression that are geared toward comfort. Or, as Ms. Biscomb put it: “Smoothening without squeezing the bejesus out of you.”

The companies may also be priming them for the future. “The thing with women’s bodies is that they are ever changing,” said Ms. Biscomb. “You accept it the way it is, then you have a baby, or menopause, and it’s like boom! You need to learn to love it again, and sometimes you need to have extra help with that.”

Silicon Valley investors have been bullish on the category. In the summer of 2018, Honeylove, a shapewear company, received funding from Y Combinator, a start-up accelerator. Betsie Larkin founded the company three years ago in San Francisco, after becoming “obsessed” with finding good shapewear during her career as an electronic dance musician, when she’d wear it nightly for shows.

“Shapewear isn’t something you can really feel proud wearing,” Ms. Larkin said. “I felt that shapewear should be really beautiful too and make you confident from the inside out, versus being something like a sacrifice.”

Facebook and Instagram are the company’s biggest marketing channels, because these platforms allow for video demonstrations of the product. “What really works for people is to just cut to the chase,” Ms. Larkin said. “We show how the product works by showing body types people can identify with, versus using the skinny models the old-school brands are still using.” (In fairness, Spanx has a plus-size division.)

That everyone is now used to frank body pictures online has also changed the way shapewear is being sold. “We’re going to show women the way they are,” said Ms. Biscomb of Shapermint. “Women are prepared to see themselves reflected on social media.”

But Is It Body-Positive?

Alexis White, a 26-year-old business analyst living in Atlanta, started wearing shapewear last summer after an onslaught of Instagram ads caught her attention. Ms. White, who has a 3-year-old daughter and described herself as “very pro-feminism,” said she doesn’t believe wearing shapewear conflicts with her values.

“If I feel beautiful and powerful walking into my workplace, if it makes me feel good, then why shouldn’t I wear it?” she said. “That’s not where my focus on feminism is.”

Kennedy Crouch, a 24-year-old podcaster living in Hamilton, Ohio, began wearing shapewear daily in high school. “It felt like protection in a way — it was like one more layer of makeup, one more thing that changed something that I didn’t like about myself,” said Ms. Crouch, who is nonbinary and uses the pronouns “she” and “they.”

Around four years ago, Ms. Crouch made a conscious decision to stop using shapewear and wear less makeup. “Part of it was I didn’t want people to be making money off of my insecurities,” they said. Though Ms. Crouch was self-conscious before wearing shapewear, they said wearing it created new insecurities, resulting in a “compulsive need to have something sucking me in.”

While Ms. Crouch still might consider wearing shapewear on a night out, they expressed skepticism over the “corporate empowerment” pervasive in the shapewear ads they see popping up on social media. “I worry about women finding empowerment in these things that are ultimately made by companies that don’t want them to feel empowered, ” they said. “I think sometimes empowerment might be confused with a feeling of getting closer to societal ideals.”

But CeCe Olisa, a blogger and co-founder of the Curvy Con, a multiday event dedicated to plus-size fashion, wears shapewear daily, occasionally doubling up (an experience she described as “intense”) to smooth out lines and give herself a “snatched waist.” As an influencer, she’d received enough questions from followers on the subject to devote one of her newsletters to an in-depth shapewear guide, which still remains one of her most popular posts to date.

“There is a portion of the body positivity community that feels that shapewear is not a body-positive thing to wear,” said Ms. Olisa, who is in her 30s. “For me, if I’m in a meeting trying to fight for plus-size women with the work I do and I’m worried about my back fat, that is not a body-positive moment.”

Some followers have reached out to Ms. Olisa, explaining how they removed shapewear from their life as a part of their “body positivity journey.” One follower described in an email how she found herself “dressing around her rolls” as a result, wearing baggier clothing and ultimately ended up hiding her body more. The decision to wear shapewear, Ms. Olisa said, should be guided by personal preference, not “because it’s about the male gaze or body-positive.”

“I’m more inclusive with my body positive philosophies,” she said. “My community wants a body-positive reality, and I’m down for that world, but I don’t live in it right now.”

Swimming With Sharks

Last August, a handful of soft-red posters popped up across the London tube, bearing the question, “Shapewear is anti-feminist, right?”

It was one of Heist’s ad campaigns. Mr. Darbyshire, the C.E.O., said that he had seen the amount of money companies poured into “proper science” researching and developing technological advancements in sportswear. “Compare that to an industry that produces garments women wear all day, every day, and there’s no R & D,” said Mr. Darbyshire. (An exaggeration, but certainly most shapewear companies are advertising what they do for curves, not their technology.)

“Spanx’s genesis is in the 1990s, their view of how their products should help you comes from a period that seems like a very long time ago,” Mr. Darbyshire said. He set out to build a brand that “does for underwear what Nike does for sportswear.”

Fiona Fairhurst, Heist’s vice president of innovation, invented Speedo’s famous Fastskin suit, modeled after sharkskin to help Olympic athletes swim faster.

“Fastskin was the first shapewear I ever made in a way,” said Ms. Fairhurst. “‘Does my bum look big in this?’ was the first question athletes asked with the sharkskin suit.”

Heist’s aesthetic is informed by the athletic, she said. “I’m not trying to create a Jessica Rabbit figure or waist training, I just want women to feel comfortable in their bodies.”

Still, younger employees have started conversations about feminism in the office, said Ms. Fairhurst, questioning comparisons to corsets and whether the company is “conforming and trying to create an ideal shape.”

Recently, Ms. Fairhurst’s 10-year-old daughter read a book on the designer Coco Chanel, who revolutionized dressing for women in the 1920s when she introduced a suit inspired by men’s wear. “Coco saw that women couldn’t move,” she told her mother excitedly. “You’re solving a problem Coco Chanel tried to solve a hundred years ago!”

At an academic conference in 2017, Maria Carolina Zanette presented a research paper on the evolution of shapewear from Victorian-era corsets to Spanx. But first, she had to explain to some male colleagues in the audience what it was.

She mentioned the concept of the “invisible corset”: how even if women abstain from wearing physically binding clothing, they are still urged to structure their bodies through plastic surgery, diets and exercise.

In interviews for her research, women described the bruises they’d gotten while wearing shapewear and recounted their experiences wearing the garments in sweltering heat. “They acknowledge it’s uncomfortable and causes bruises in your skin, how if you go out with it you basically can’t eat or do anything,” she said. “But then on the other hand, the person will say, ‘I felt I was putting on armor.’”

While a suit of armor offers protection, historically, the metal was cumbersome; it made its wearers weary. And when it comes to shapewear, it’s less clear what people are seeking protection from. The truth of their own bodies?

I admired how sleek my clothes appeared in the mirror while wearing shapewear. But I also didn’t feel particularly warrior-like when I couldn’t focus at my desk, unaccustomed to the discomfort caused by the constricting garment.

The only real moment of empowerment came when I took it off.