Boobs . The Femme Den talks about them easily and often — and about the challenges they present to designers. Backpack makers don’t seem to have a clue what to do about boobs. Ditto designers of unisex hospital scrubs, famous for their gaping V-necks. “One surgeon told me there wasn’t a woman at the hospital whose boobs he hadn’t seen,” says Femme Den member Whitney Hopkins.

A design engineer at Smart Design, Hopkins is also one of four members of the Den, an internal collective at the firm that’s devoted to thinking about the bodies and brains of women and how to design — smartly — for them. I ask the group, which consists of Hopkins, Agnete Enga, Erica Eden, and Yvonne Lin, if that means razors and sports bras or if it means rethinking everything. “Both,” they answer in unison, from a nook of Smart’s loftlike Chelsea offices. Women are not a niche market, they insist (“No one likes to be targeted,” sniffs Eden), but companies should also be careful not to confuse equality with sameness.

“When most people think of designing for women, they automatically think of tampons and birth control,” Lin says. (It doesn’t help that in industrial design, females make up just 20% of the field.) “Even when a lot of companies think that a product is for both genders, in reality they’re just designing for men. Design is male-biased. Designers are working with male procedurals, probably going back to the beginning of time.” Now, the Femme Den is looking to inject some femininity into those procedurals, everywhere from U.S. Army bases to Target, BP, and Nike.

Like most things at 30-year-old, 130-member Smart Design, the Femme Den bubbled up from an interesting problem. In 2005, Nike’s women’s watches weren’t hitting sales expectations. The all-male design team hired two Smart female staffers (they would become founding members of the Den), who discovered that Nike’s target demographic was begrudgingly opting for clunky men’s watches because they offered more athletic features. When Nike beefed up its women’s watches’ capabilities and fine-tuned a sleek, sporty aesthetic, sales quickly boosted. “It was eye-opening,” says Enga.

As the group took shape, Smart Design cofounder Dan Formosa (affectionately dubbed “Femme Dan”) encouraged the women to “think radically.” They began gathering on weekends, eventually taking their name from a cheekily labeled file folder. When the Femme Den was accepted to the International Conference for Universal Design, in Kyoto, Japan, in 2006, the underground gaggle came out to the world.

The Femme Den isn’t a separate division at Smart Design. Instead, Hopkins, Enga, Eden, and Lin work on shifting teams, deliver in-house presentations, write white papers, and infuse the firm with their ideas. And as more companies realize the potential in the female market — a recent study showed that women influence 80% of household purchases — the group is added ammunition for attracting clients. “If you talk about the differences between men and women at a corporate human-resources meeting, you’d be fired or sent to diversity training,” Formosa says. “But when we cover that same ground with large corporations, the discussion just lights up. There is so much need there, it hits a nerve.”

Companies recognize the need, but most are clumsy — if not patronizing — in their attempts to address it. This often leads to what the Femme Den calls the “shrink it and pink it” reflex, the kind of mindless design that produces such works of genius as mini pink tool kits and Dell’s pastel-saturated Della Web site, stocked with tips about “finding recipes” and “counting calories.” (Dell dumped Della within two weeks of its launch.) What women really want, the Femme Den argues, is intuitive design. In a Yale University study, 68% of men asked to program a VCR using written instructions were successful, compared to just 16% of women. That doesn’t mean women are less intelligent than men (please), but that they’re less tolerant of complicated interfaces — more willing to skip new tech than to slog through manuals. “Men will walk into an electronics shop and look at the white cards that list the features. Women will pick up the cameras, flip them around, and look at the buttons,” Lin says. “They want to know: Is it intuitive?”