Shopping for bras and underwear may be the mall equivalent of going to a chick flick: It's a very female space and women want it to be just so.

The new aerie store opening this weekend at South Hills Village is meant to be just so. There's a daybed with piles of pillows, mirrors for trying on makeup and a dressing room where friends in side-by-side spaces can share opinions on clothes.

"It just feels like a place you want to hang out with your girlfriends," said Betsy Schumacher, chief merchandising officer for aerie.

A few Wall Street analysts may wander through here, too, since this concept is looking like the next big thing for South Side teen retailer American Eagle Outfitters.

Just a year ago, the retailer opened three aerie stores devoted to the undergarments and the comfortable "dormwear" pieces it had been offering in its well-established namesake stores. The concept did even better than expected, racking up $100 million in sales the first year, according to a report by FBR Research.

"We knew we had something that we had to run with," said Ms. Schumacher. Now the company plans 100 aerie stores by the end of next year. The chain eventually could support between 400 and 500 stores with sales around $1 billion.

The attraction for shoppers -- and by extension, investors -- is not just the polka-dot bras or the colorful, holiday undies that say, "All wrapped up." There are robes, leggings, hoodies, sweaters, camisoles and pajama pants that constitute what the company calls dormwear, or clothes that young women might wear around college dorms or even to class.

Last week, the retailer officially launched a new line of fitness and workout clothes that it is calling aerie f.i.t. One wall of the new store is devoted to bright runner jackets, shorts, pants and workout accessories that use the kind of technical fabrics more typically found in sporting goods stores or shops for yoga students.

Before Thanksgiving, aerie will launch personal care products, including bath and body items, cosmetics and candles. Sometime next year, aerie is expected to add personal fragrance, too.

Ms. Schumacher said the fitness line evolved from "closet interviews," where researchers go to girls' homes, look in their closets and ask how they use their clothes.

A common problem surfaced in finding attractive workout gear that could do things such as preventing overheating and pull moisture away from the body. "She [the typical customer] wanted to look cute but she wanted to have fitness apparel that performed," said Ms. Schumacher.

Tom Filandro, specialty retail analyst with Susquehanna Financial Group, called that "potentially a very explosive opportunity," and not just for American Eagle. He noted other retailers are starting to discover the interest in more stylish fitness wear. He could see American Eagle, Abercrombie & Fitch and Victoria's Secret all competing in that arena soon.

Like SUV owners who never take their vehicles off-road, even customers who aren't serious fitness buffs like the look of workout clothes, said Mr. Filandro.

Meanwhile, American Eagle's emergence as an underwear purveyor coincides with increased interest among many retailers in the business sometimes called "intimates" and other times referred to as "foundation garments," both terms that harken to the days when such things were not to be seen outside the dressing room.

Victoria's Secret has long proven money can be made there. More recently companies such as J.C. Penney and Kohl's have launched new underwear lines. The Victoria's Secret line called PINK, which targets a younger customer, has been very strong.

Since the beginning, officials have described aerie as "sweetly sexy," rather than either vampy or strictly functional.

The key to the line's success, Mr. Filandro said, will be maintaining the "maniacal" attention to the fit of bras and underwear that American Eagle has long applied to its jeans. Another of the retailer's growth initiatives, a chain named Martin + Osa that targets older shoppers, has struggled in part because of fit problems, he said.

Mr. Filandro believes aerie benefited in a subtle way from the retailer's decision not to wait around for locations near its namesake stores. At South Hills Village, the American Eagle store is downstairs on the first floor, while aerie is on the second level.

When it comes to bras and underwear, female shoppers like having their own space, he said. Side-by-side locations, such as the one originally set up at Ross Park Mall, don't offer quite the same feel. "She's much more comfortable in her own environment."

Distance from the very youth-centric American Eagle also has opened the door to shoppers a bit above the 15- to 25-year-old target customer, he said. "We've witnessed 30-plus women shopping that store." That's an opportunity but also a risk. Too many older shoppers could make it feel less like a place for teens to hang out.

Hanging out seems to be what the new white-and-cornflower blue dressing room in the prototype store is all about. Seven fitting cubicles open off a central space anchored by a large cushioned seat. Some are set up as suites, where friends can open their doors to each other but still have a curtain for privacy from the main seating area.

Each cubicle has a small button with the aerie signature bird logo. When pushed, the button alerts an employee that someone needs help. Small flashing birds outside the cubicles track the order in which customers called for help.

A wooden armoire in the central dressing room area holds trays of bras organized by size so any customer easily can try on all the different bra designs in the store available in her size.

The dressing room helped increase the size of the prototype. The original stores covered 2,400 square feet, with subsequent locations boosted to 3,500, said Ms. Schumacher. At South Hills Village, the aerie store fills 4,144 square feet.

Although the store is designed with young women in mind, Ms. Schumacher said mothers and boyfriends don't seem afraid to walk in. Still, for those who just can't get comfortable going into a store selling bras and underwear, the company has thoughtfully placed a wooden bench just outside the shop's glass front door.