The Data Scientist Who Reinvented Bra Sizing
Heidi Zak looked at the bra industry and saw a math problem. The standard sizing system — A, B, C, D cups in band sizes jumping by two inches — was designed in the 1930s and hadn't been meaningfully updated since. It forced millions of women into approximate sizes, choosing between "too small" and "too big" without ever finding "just right."
Zak's solution was elegant: half-cup sizes. It sounds obvious. No one had done it.
The Google Background
Born in 1981, Zak came to lingerie from technology, not fashion:
- Studied at MIT and Duke's Fuqua School of Business
- Worked at Google in strategy and operations
- Worked at Aeropostale on digital commerce
She brought a data-driven mindset to an industry that had historically relied on tradition, intuition, and — frankly — guesswork when it came to fit.
The Fit Problem
Zak's research revealed staggering numbers:
- 80% of women wear the wrong bra size
- The average woman tries on six different bras before purchasing one
- Bra returns are among the highest of any apparel category in online retail
- Women lose an estimated $15 billion annually on bras that don't fit properly
The problem was not that women didn't care about fit. It was that the sizing system was too crude to serve them.
ThirdLove and Half-Cup Sizing
Zak co-founded ThirdLove in 2013 with her husband Dave Spector. The brand's innovations included:
- Half-cup sizes (AA, A, B, C through H, in half increments) — effectively doubling the number of available sizes
- The Fit Finder Quiz — an online questionnaire that used data science to recommend a size, eliminating the need for in-store fitting
- Try Before You Buy — customers could wear a bra for 30 days and return it if the fit wasn't right
- A direct-to-consumer model that bypassed department stores and their limited size inventories
The Victoria's Secret Challenge
In 2018, ThirdLove took out a full-page ad in the New York Times responding to Victoria's Secret CMO Ed Razek's comments about the VS Fashion Show not needing transgender or plus-size models. The ad, addressed directly to Razek, stated:
"We're done with the fantasy. We want to create a world where the customer comes first."
The ad was a cultural moment — a direct-to-consumer startup publicly challenging the industry's dominant player on values, not just products.
The Numbers
- ThirdLove has raised over $68 million in venture funding
- Ships millions of bras annually
- The Fit Finder Quiz has been taken by over 17 million women
- Expanded beyond bras into underwear, sleepwear, and loungewear
Why She Matters
Zak proved that the lingerie industry's sizing problem was not intractable — it was just unaddressed. By applying data science to a problem the industry had accepted as inevitable, she demonstrated that technology could improve the most intimate aspects of women's daily lives. Half-cup sizing is now offered by multiple brands. The Fit Finder model has been copied across the industry.
She looked at a 90-year-old sizing system and asked: why not add halves?