A couple of weekends ago, I was waiting on a sofa in a communal changing room, while my teenage daughter was trying on clothes, when the young woman who had been behind us in the queue for cubicles – I had noticed the yoga mat and hardback copy of Margaret Atwood’s The Testaments sticking out of her fabric tote bag championing a charity for girls’ education – emerged barefoot in a short black dress. She stood sideways in front of the big mirror, wrinkled her nose at her reflection, sucked her tummy in hard and then, happier, smiled at me. “Just needs Spanx, right?” she said.

Correct answer to that, anyone? Because I was stumped. My first instinct was: of course you don’t need Spanx. You are a twentysomething peach, you are perfect exactly as you are and that’s enough of that nonsense. But then I thought: maybe it’s kind of great that you can talk openly about wearing whichever big, sturdy knickers work for you and not feel as if you have to pretend to be wearing lace lingerie all the time. Then I thought: hang on a minute. Why am I plotting this young woman on an imaginary feminism graph with “books read” on the X-axis and “knickers worn” on the Y-axis?

You know that feminism graph … oh, yes you do. It may be made up, but it is, at the same time, very much a real thing. We map women’s progressive credentials against the height of their heels (too high being unsisterly) or the length of their eyelashes (fake, ditto). The coordinates don’t always involve fashion – but they frequently do. And underwear, being the point where women’s bodies meet the outside world, is very often a flashpoint.

Facebook Twitter Pinterest SKIMS, by Kim Kardashian West.

In the past decade, Victoria’s Secret has become the Fox News of fashion’s attention economy. It turned women’s bodies into luridly compelling content, and in doing so turned underwear into a political battleground. This year, having been persistently criticised for fetishising an aesthetic of ultra-low body fat, a Victoria’s Secret advertising campaign features a plus-size model, Ali Tate Cutler, for the first time. Last week, it announced that it would be cancelling its annual fashion show (which had also been criticised for its unrealistic portrayal of its models).

On the face of it, shapewear is at the opposite end of the underwear spectrum to Victoria’s Secret. Control pants are utilitarian, shadowy items of doubtful beauty, while catwalk-worthy lingerie is designed to be seen, to dazzle and titillate. But they share a mission, which is the pursuit of an ideal, hourglass-curve body. Now, the size-inclusivity and body-positivity movement that puts Lizzo on the cover of next month’s British Vogue is having an impact on the shapewear sector of the underwear market, too – but not in the way you might have expected.

The mood music around underwear has seen squished-together cleavage replaced with comfy bralets in ad campaigns, and Beyoncé striking a queenly pose on Instagram in a burgundy bra, turquoise satin knickers, baby bump and veil. But, far from throwing out their control pants and accepting their squidgy inner thighs and potbellies, millennials are driving a shapewear boom. A recent report by the business analyst Textiles Intelligence predicted that the global market for shapewear will expand at an annual rate of 4% a year between now and 2022.

Women tell us constantly how confident they feel wearing our shapewear Heist's Fiona Fairhurst

Kim Kardashian West entered the market this year with her “solutionwear” range, SKIMS – a name whose phonic adjacency to Spanx is unlikely to be an accident. Whatever your views on the Kardashians, you will acknowledge that, when it comes to pop culture, their money-making instincts are rarely wrong. The fashion search engine Lyst reports that searches are up year on year in shapewear for biker shorts (137%) and bodysuits (83%). Oprah recently started a frenzy for the Perfect Black Pant by Spanx – a pair of trousers with inbuilt tummy and thigh control – when she included it on her annual holiday-season wishlist of Favourite Things, gushing that she had called Spanx’s founder, Sara Blakely, to applaud and thank her for creating the “ultraflattering” trousers.

Heist, a cult tights and shapewear label that prides itself on skin-tone inclusivity, and recently launched sustainable fishnet tights, has tackled the issue head on with a series of posters that posed the question: “Shapewear is anti-feminist, right?” and invited consumers to discuss on social media. “We posed that question because we hear it a lot – the idea that shapewear is the modern corset, and therefore anti-feminist,” says Fiona Fairhurst, the vice-president of innovation at the brand. “The response to the campaign was huge. People really engaged. There were those who challenged us on the basis that the shapewear industry perpetuates the idea of a ‘perfect’ body, and we had a really interesting panel that delved into how much we alter our appearances for ourselves and others. For us, it’s about personal choice without judgment. But, let’s be clear, we don’t think that wearing shapewear is a feminist act akin to fighting for equal pay or challenging gender representation.”

Facebook Twitter Pinterest Perfect Black Pant by Spanx.

Brands such as Heist and Rihanna’s Savage X Fenty lingerie claim that by being inclusive to a spectrum of skin tones and range of body sizes – at point of purchase, but also in advertising imagery and in Rihanna’s case on the New York fashion week catwalk – they are disrupting the shapewear and lingerie worlds with an authentic celebration of all women. “Women tell us constantly how confident they feel wearing our shapewear,” says Fairhurst. Heist’s language is that of empowerment: a “better experience”, a collection that “works for everyone and has comfort front of mind”.

Whether or not shapewear has truly developed in philosophy, it has evolved technically. I can report that the new generation of products from Heist and Spanx are infinitely more comfortable than control pants were in their original iteration. Advanced fabric technology allows pressure to be evenly distributed through a wide waistband. The rigid seams that once dug tightly into flesh, a daylong reminder of the very bit of your body you were trying to magic away, are no more. Spanx leggings, with seamless legs and a flattening power waistband, have a surface grace, which belies their engineering. Fairhurst made her name with Speedo’s Fastskin, a swimsuit inspired by sharkskin, which attempts to emulate the ability of a shark to travel through water with about 10% less energy expenditure than a fish with smooth skin. At Heist, she uses “HeroPanel” technology, which mimics fascia, the body’s connective tissue that sits between muscle and skin, to provide “a natural support system” that can lift as well as compress – essential for a generation that wants a high, prominent bottom as well as a small waist.

“At a fundamental level, our shapewear is comfortable, looks good and doesn’t make you sweat. The HeroPanels have 20,000 laser perforations, making them 100% breathable,” says Fairhurst. “They also take up to 5cm off your waist in total comfort,” she adds, “if that’s what you’re looking for.”