Stephanie Thomas stared down the video camera, steeled to shed her clothes and share her deepest insecurities with a roomful of strangers.

Her audience at Zen House on the Lower East Side of Manhattan had arrived late last month for an open call to participate in a YouTube project called “What’s Underneath.” It was organized by Elisa Goodkind and Lily Mandelbaum, the mother and daughter who are the fashion impresarios behind a multimedia venture encompassing StyleLikeU, a popular website, and its offshoots on YouTube — and most recently, a book. Its message is explicit in its title, “True Style Is What’s Underneath: The Self-Acceptance Revolution.”

Self-appointed style-world evangelists, Ms. Goodkind, 59, and Ms. Mandelbaum, 27, gently prodded their subjects to talk about the emotional struggles and idiosyncrasies that underpinned their fashion sense. They aimed, Ms. Mandelbaum said, “to encourage people to value the things that make them different, even the things that they might hate about themselves — they’re what make you unrepeatable.”

Ms. Thomas, who is 47 and works at Trader Joe’s, seemed to have gotten the memo.

Ms. Goodkind asked Ms. Thomas when she last cried, and urged her to peel off her leggings. She obliged. Reduced to her brassiere and rose-tinted panties, she recalled that a recent visit to her former home in Baton Rouge, La., brought her to tears. “I was missing the sense of community,” she said. “You don’t find that much here.”

What was her favorite body part?

“My boobs are my favorite and least favorite,” she said, unabashed. Sure, her sizable breasts often drew unwanted stares. “But I love them, because they’re mine.”

Deft at pushing emotional levers, Ms. Goodkind, a former fashion stylist, and Ms. Mandelbaum, a documentary filmmaker, pressed on, encouraging visitors, some of whom had responded to online invitations — others who had simply wandered in from the street — to step to the makeshift stage, strip off their clothes and, with them, psychic inhibitions. The filmmakers’ ultimate goal is to showcase diversity in its myriad forms: racial and ethnic backgrounds, gender or sexual orientation, age and size. That last was of particular relevance to Ms. Mandelbaum, who struggled with her weight as a teenager.

“My mother was less accepting of my body at the time,” she recalled, adding quickly that Ms. Goodkind began changing her tune when the two began their project nearly a decade ago.

Their book, an outgrowth of interviews, many of them taped over that time, focuses on style mavericks like Fatima Robinson, a video music director and choreographer, who vamps for the camera in the jeweled and feathered headdress she wore for her visit to the Burning Man festival the year she turned 40. “Before that I would have been too stuffy,” Ms. Robinson said. “Now I’m at a place where I can allow myself to let go.”

And there is Gail Chovan, a designer and teacher in Austin, Tex., who after a double mastectomy rejected breast reconstruction and the padded brassiere her mother had urged her to wear. “I’m feminine, and I don’t have to wear a padded bra to show that,” Ms. Chovan said as she posed in a tank top and a series of embroidered vests.

The former booking agent Bethann Hardison, a pioneering African-American model in the 1970s, posed gamely in a purple bra and boy-cut panties. “This isn’t senior citizen time for me,” she declared. “The revolution ain’t over.”

Such accounts are especially resonant in a sociopolitical climate that can be unwelcoming, if not downright hostile, to difference. “This project goes so much deeper than talking about style,” said Ellen Nidy, managing editor at Rizzoli, the book’s publisher. “It went into the vulnerabilities and hangups of people who didn’t necessarily fit with societal norms of what’s beautiful, what’s fashionable. They were redefining all that for themselves.”

That disruptive approach is reflected on the book’s cover. Together, its subjects — they include Cathy Cooper, a 60-something former heroin addict, now an artist in Los Angeles; Rachel Fleit, a filmmaker who flouts her baldness for the camera; and Alok Vaid-Menon, a transgender writer and performance artist garbed in a dress — form an eye-opening mosaic.

An exercise in extreme casting, the book underscores an inclusiveness in tune with the fall 2017 runway shows in New York that, however fitfully, showcased models of varying races, ethnicities, gender preferences and, in particular, size. No fewer than 26 plus-size models strode the catwalks in February.

Yet a similar inclusiveness was not reflected in the fashion advertising campaigns shot during that period. A tally by the Fashion Spot website cited 24. Five percent of models cast were African-American, Hispanic or Asian, an increase of only one percentage point over the previous year. Plus-size models made up only 2.3 percent, and in only two prominent instances was a model over 50 selected for a major campaign, both with the 73-year-old Lauren Hutton.

In the light of such numbers, the book and the filmmakers’ open call seemed all the more timely — even urgent, they might argue. “We want to show what’s vulnerable, what’s honest in these people’s stories,” Ms. Mandelbaum said. “We’re hoping to subvert a culture that promotes a standard of perfection that most of us can never attain.”

Their ultimate goal, Ms. Goodkind added, is to demystify fashion and to promote self-discovery through the not-so-simple ritual of getting dressed. “The process can be messy,” she allowed. “But there’s beauty in that.”