Another online business that's zeroing in on the plus-size market is Gwynnie Bee, an online-only subscription website that allows women to rent clothing.
The service offers plans that vary from checking out one item at a time each month, for $35 a month, to 10 items out at a time, for $159 a month. If women fall in love with an item, they also have the option to purchase it. The site launches new arrivals a few times each week, and houses more than 2,000 total styles, CEO Christine Hunsicker said.
"In a rotational model, the only question that you have to answer is, 'Do I like it enough to try it?'" Hunsicker said.
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Although Gwynnie Bee does not disclose its membership figures, Hunsicker said its subscription base has grown 10 to 15 times in the last 10 months. What's more, over 50 percent of users who test out the site through its free trial service join the site.
But the store is not just about experimentation—it's also about serving a customer who often prefers to shop online, and whose size swings more dramatically than that of thinner women.
"Most women have multiple sizes in their wardrobe because there is a decent amount of weight fluctuation throughout the year," Hunsicker said. "You can use the service as you're moving up and down the spectrum."
Despite their target shopper's penchant for online, bricks-and-mortar stores aren't excluded from the plus-size boom. Retailers such as Target and Wal-Mart offer larger sizes, while Ascena Retail Group's Lane Bryant and Catherines stores have the largest hold on the market in the specialty store industry.
Lane Bryant has been working to freshen its image among plus-size shoppers. Most recently, it collaborated with fashion designer Isabel Toledo on a line of clothing, and announced an upcoming lingerie tie-up with designer Sophie Theallet.
It's a change of pace that led the brand to an 8 percent same-store sales gain in the quarter ended Jan. 25, and sales of $278.7 million.
"[Our customer] wants the confidence that all women want. She wants the fashion that all women deserve," Lane Bryant CEO Linda Heasley told CNBC earlier this year.
"Our responsibility is to put the fashion industry on notice," she said.
—By CNBC's Krystina Gustafson.