The Data Scientists Who Reinvented the Bra
A Google Executive's Frustration (2013)
Heidi Zak was a former Google and Aeropostale executive when she had the experience that would launch ThirdLove: she could not find a bra that fit. Despite decades of innovation in every other category of apparel, the bra industry was still forcing women to choose between cup sizes that were either too big or too small.
Zak and her husband Dave Spector, a former Google data scientist, founded ThirdLove in San Francisco with a deceptively simple thesis: if you could measure women more accurately and offer more sizes, you would build a better bra company.
Half-Cup Sizing: A Small Innovation with Massive Impact
ThirdLove's signature innovation was the introduction of half-cup sizes. Instead of the traditional A, B, C, D system, ThirdLove offered A, B, B+, C, C+, D, and so on — effectively doubling the number of available sizes. The insight was backed by data: their fitting algorithm revealed that roughly 30% of women fell between traditional cup sizes.
The Fit Finder Quiz — an online questionnaire that used data science to recommend the perfect size — became ThirdLove's most powerful tool. Over 17 million women have taken the quiz, generating a proprietary dataset on women's bodies and preferences that no competitor could match.
The Full-Page Letter to Victoria's Secret (2018)
In November 2018, after Victoria's Secret's Ed Razek made dismissive comments about inclusive sizing, Heidi Zak took out a full-page advertisement in the New York Times. The open letter, addressed "Dear Victoria's Secret," directly challenged the incumbent:
"You market to men and sell a male fantasy back to women... We believe the future is built on a dream. One where women are their own heroes."
The letter went viral. It crystallized the cultural moment — the old guard's definition of beauty was crumbling, and a new generation of brands was ready to replace it.
Growth and Challenges
ThirdLove raised over $68 million in venture capital and expanded from its DTC origins into Nordstrom and other retailers. The brand eventually offered 80+ sizes, making it one of the most size-inclusive bra companies in the market.
The company faced the same headwinds as many DTC brands — rising customer acquisition costs, the challenges of physical retail, and intense competition. But ThirdLove's data advantage and loyal customer base provided resilience.
Legacy
ThirdLove's contribution to the lingerie industry extends beyond its products. The brand proved that data science could solve problems that intuition and tradition had failed to address. It demonstrated that "fit" was not a luxury but a right, and that the bra industry's limited sizing was not a manufacturing constraint but a failure of imagination.