It’s little wonder that Mormons express strong and varying opinions about what is stylish and acceptable. The rapidly growing religion counts more than six million members in the United States (30 percent of them in Utah), and individuals have long had to balance tradition with a desire to fit in with the culture at large. Members still battle a perception of otherness, as in the recent flare-up between Mr. Romney and Robert Jeffress, a Southern Baptist pastor and Rick Perry supporter who derided the religion as a “cult.”

Needless to say, countless Mormons work in fashion, design, art, music and film, and they generally dress and act just like anybody else.

But when it comes to dressing young and hip, some Mormons said they face unique challenges. Among other things, many adult Mormons wear a type of underwear known as the temple garment, meant as a symbolic reminder of an individual’s promises to God. Both men and women have their own style of garment, but each consists of two pieces, a chaste knee-length bottom reminiscent of a boxer-brief and a white undershirt.

Jeggings and maxi dresses aren’t an issue, but tank tops and short skirts are, said Elna Baker, Britain Baker’s sister who detailed her struggles with the faith in a 2009 memoir, “The New York Regional Mormon Singles Halloween Dance.” To cover up the undergarment, some style-conscious Mormons in places like Brooklyn adopt a retro-ironic look from thrift stores, including “Mad Men”-style dresses, or a kind of ’80s secretary look: ruffled blouses, bow collars and high-waisted pencil skirts. “It’s very much a Zooey Deschanel look,” said Ms. Baker, who left the church after her book was published.

As a writer living in Brooklyn and veteran of the Moth storytelling gatherings, Ms. Baker, 29, found herself in the center of a growing Mormon subculture, populated by creative types who dress like they stepped out of “a modest American Apparel ad,” she said. Striped shirts, cardigans and horn-rimmed glasses are part of the uniform.