Shoppers can use a "Fit Finder" tool on ThirdLove's website to find the right bra size. It is one of the start-ups funded by former AOL CEO Tim Armstrong as he bets big on a consumer pivot away from big tech platforms to direct retail sales.

Missteps at L Brands' Victoria's Secret are opening up the door for other lingerie retailers to tap into an underserved market.

Today's female consumers are increasingly turned away by Victoria's Secret overtly sexy image. The brand was made famous for its brightly colored push-up bras, but shoppers are now in search of comfort and fit. A handful of bra and underwear upstarts are gaining ground by being more inclusive.

Victoria's Secret has long dismissed the idea of expanding its size range for bras to include more women. Its website only has a slightly broader assortment than its stores. In turn, new players ThirdLove and Adore Me are looking to scale their businesses, which are built around selling extended sizes of bras in softer, neutral colors.

Sales of women's bras in the U.S. held steady at nearly $7 billion last year, according to NPD Group. Full-figure sizes (38+), meanwhile, are a steadily growing segment but with not a lot of sellers, the retail tracking service found.

"The underserved full-figure and plus-size market continues to be one of retail's major merchandising mistakes," said Marshal Cohen of NPD Group. "With retailers focusing on assortment productivity, brands adding new styles become a harder sell, ... but size extensions are a straightforward way to expand on successful existing assortments."

There really couldn't be a better time to grow in the space. ThirdLove and Adore Me are taking advantage of that.

ThirdLove, a lingerie brand based in San Francisco, said Wednesday it's rolling out extended bra sizes this month to include bands ranging from size 28 to 48, and cups from AA to H. The online retailer said it did a beta test of the new options last year, and they sold out in a little more than a week. With the launch, ThirdLove will now offer more sizes than other rivals including Calvin Klein and American Eagle's Aerie.



"I do think there is no choice but to become more inclusive," ThirdLove CEO Heidi Zak told CNBC. "I think the [lingerie industry] is one of the most old-school industries in apparel that's out there."

Another up-and-coming player in the lingerie space, Adore Me, is planning to open hundreds of stores in the U.S. over the next few years, aiming at Victoria's Secret's real estate — its more than 1,100 shops in North America, many within suburban shopping malls.

Adore Me, which asks shoppers to take a style quiz online before browsing its website, just opened its first store at GGP's Staten Island Mall in New York last week.

"We don't have any images of ... retouched women that are typically not relatable," CEO Morgan Hermand-Waiche told CNBC. "Our store is very colorful when Victoria's Secret is very dark usually and it looks like you are going to the club."