ThirdLove CEO explains how the start-up is thriving as Victoria's Secret struggles

• ThirdLove CEO Heidi Zak tells CNBC's Mad Money how her start-up uses data to help women find the bra that fits them perfectly.
• Unlike L Brands and its struggling brand Victoria's Secret, ThirdLove has embraced data, which influenced its decision to launch 24 new sizes this summer.
• Zak also said the company is looking into decreasing its Chinese sourcing.

As L Brands' flagship brand Victoria's Secret has struggled to attract customers, start-up ThirdLove has turned selling women's intimates into a profitable business since its founding in 2013.

ThirdLove CEO Heidi Zak attributes the waitlist of more than a million women waiting for one of its bras to the reason why the company decided to launch 24 new bra sizes this summer: data.

Heidi Zak, Co-Founder and Co-CEO, ThirdLove

Scott Mlyn | CNBC

Earlier this year, in an interview with the Financial Times, L Brands CEO Les Wexner was dismissive about the usefulness of data and algorithms when it comes to predicting what women want to buy.

But Zak disagrees. No stranger to using data, she quit her job at Google to start ThirdLove.

Zak told CNBC's Jim Cramer that ThirdLove built its business using data and uses data to inform every decision, from product development to targeted marketing.

After all, data inspired the company to create half-sizes for bras because their data found that a sizable portion of their customers were between sizes. Customers find their perfect ThirdLove bra by answering a series of questions on the San Francisco-based company's website.

"Using the data that we collect and algorithms that we've developed internally, we'll recommend her size down to the half-cup and the style meant for her body," Zak said. "So with every woman who does our Fit Finder, we get smarter and smarter, and we've had over 10 million women do our Fit Finder."

While ThirdLove has no shortage of customers looking to buy its bras, underwear and sleepwear, the company is tackling one obstacle that many other apparel-makers are also facing: U.S. tariffs on Chinese imports.

The ThirdLove CEO told the Mad Money host that the start-up currently sources about 50 percent of its manufacturing from China. Zak said that the company is working on changing that, but she did not provide a more specific timeline.

Watch the full interview:

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