ThirdLove’s 2025 Triumph: 78 Sizes, Data, DTC, and Devoted Fans

Explosive E-Commerce Growth and Loyal Fans

ThirdLove has quietly become a powerhouse in online intimate apparel, with its e-commerce revenues surging into the tens of millions. In 2024, their flagship site hit $69 million in revenue, and projections for 2025 suggest continued growth to a range of $72 million to $76 million. A recent benchmark report shows ThirdLove’s site converting at 2.0–2.5% of visitors—impressive for the fashion retail industry. Thanks to personalized fitting tools like their proprietary Fit Finder quiz (98% accuracy), customer return and loyalty rates have skyrocketed, with an industry analysis noting that ThirdLove's repeat customer rate is around 60%—far above the typical 20–30% seen in other e-commerce segments.

This level of retention and loyalty isn’t just about great products; it’s also about ThirdLove’s data-driven focus on fit and customer experience, a strategy that has paid off. Early growth phases saw a 347% year-over-year increase in sales and a 62% YoY boost in returning customer orders. ThirdLove’s “Try Before You Buy” policy and Fit Finder quiz helped drive 20% higher conversion rates than industry norms, with more than 4 million bras sold by 2019. With viral Instagram campaigns and high-profile testimonials, ThirdLove has cemented its place as the “number one online bra brand for millennials”—and its appeal is only growing with Gen X.

Leadership Driving Innovation and Inclusion

At the core of ThirdLove’s success is a founder-led team that combines tech expertise, creative innovation, and a focus on customer-centric values. Co-founder Heidi Zak (CEO), a former Google executive, has merged the discipline of Sequoia Capital with Google-scale data, laying the groundwork for ThirdLove's technology-first approach. Alongside her husband, David Spector, a former Sequoia and Google too, they’ve prioritized building a stable and scalable tech infrastructure, ensuring that their online platform remains reliable for customers shopping for their bras and intimates.

Their creative co-founder Ra’el Cohen (CCO) has been instrumental in shaping ThirdLove’s design and loyalty programs. Under her leadership, ThirdLove introduced its multi-tier Hooked rewards program, which saw 41% of customers sign up by 2019—a strong indicator of customer engagement and retention. By offering 78 bra sizes, including half-cups, ThirdLove has unlocked a massive market of women who often find themselves overlooked by traditional sizing charts. This insight into customer needs has made ThirdLove a trailblazer in inclusivity, fulfilling the needs of approximately 60% of women who fall outside standard bra sizes.

Outpacing the Competition

ThirdLove’s rise comes amid a crowded intimates market. Legacy giant Victoria’s Secret still leads by revenue (about 22.4% market share, $5.4 billion annually), but it’s under siege. In aggregate, direct-to-consumer lingerie—led by ThirdLove, Savage X, and others—commands about 16% of the market today, up sharply from prior years.

Even smaller labels like CUUP (recently acquired by FullBeauty Brands) focus on niches, but ThirdLove’s head start shows in every metric. For example, where Victorian-era retailers offered ~30 sizes at most, ThirdLove’s 78-size arsenal vastly widens its addressable base. Its lean DTC model (bypassing mall stores) also lets ThirdLove invest more in marketing ROI instead of overhead. The payoff is clear: ThirdLove is capturing incremental sales and market share while competitors scramble to modernize.

Why Full-Funnel Measurement Will Become Key to Continued Growth

ThirdLove has already done an impressive job creating strong customer loyalty—its analytics for bra fit have helped them win over customers, leading to high repeat purchase rates and minimal return churn. However, as competition in the DTC space heats up, ThirdLove will need to extend this data-driven approach beyond just product fit. To continue growing, they will need to focus on optimizing their full-funnel marketing strategy—not just retention but the entire journey, from awareness to conversion.

This is where tools like media mix modeling (MMM) and attribution can significantly impact their marketing strategy. For example, CUUP, a competitor in the intimate apparel space, has used Fospha’s platform to better allocate their media spend across various channels, ensuring every dollar spent delivers the maximum return. Using MMM and real-time attribution models, they were able to refine their budget allocation and improve their strategy for each touchpoint in the funnel.

A standout example of this is CUUP’s 400% increase in TikTok engagement while still maintaining a strong return on ad spend (ROAS). The key to this success was Fospha’s ability to measure off-platform effects, such as the halo effect that DTC ads have on marketplace sales. These insights allowed CUUP to make smarter decisions on where to allocate their budget and optimize their performance across all platforms, resulting in stronger growth.

What Customers Are Saying

Ultimately, ThirdLove’s strength is proven by its fans. The brand consistently earns high review scores, with testers calling its bras “super comfortable” and praising soft, seamless fabrics. In Good Housekeeping trials, multiple women noted ThirdLove’s 24/7 T-shirt bra fit perfectly under clothes all day without digging in. Online, real customers echo this: one reviewer raves about “not having to constantly adjust” her ThirdLove bra, and many cite the inclusive sizing as life-changing. Demographically, ThirdLove appeals to a broad crowd. Heidi Zak herself notes the core base is millennial women (and growing in Gen X). In fact, nearly half of new buyers enroll in ThirdLove’s loyalty program, reflecting fierce retention. The brand often showcases “real” customers of all ages and shapes in its ads. As a result, ThirdLove’s social channels teem with organic word-of-mouth and testimonials, reinforcing why 60% of its purchasers become repeat buyers.

 ECDB, 2025. ThirdLove – Financial Performance & Growth Metrics. Available at: https://www.ecdb.com/brands/thirdlove [Accessed 27 October 2025].

 ECDB, 2025. ThirdLove's eCommerce Revenue Analytics. Available at: https://ecommercedb.com/store/thirdlove.com [Accessed 27 October 2025].

 Fospha, 2025. Fospha’s Full-Funnel Marketing Measurement for DTC Brands. Available at: https://www.fospha.com/marketing-measurement [Accessed 27 October 2025].

 Fospha, 2025. How Fospha Helps Brands Like ThirdLove Optimize Marketing Spend. Available at: https://blog.fospha.com/thirdlove-marketing-optimization [Accessed 27 October 2025].

 Shopify, 2025. The Leadership Behind ThirdLove: How Heidi Zak and David Spector Built a Brand for the Modern Woman. Available at: https://www.shopify.com/blog/thirdlove-leadership [Accessed 27 October 2025].

 DCF Modeling, 2025. Market Share and Growth in the Intimates Industry: Comparing Victoria’s Secret and ThirdLove. Available at: https://www.dcfmodeling.com/intimates-industry-market-share [Accessed 27 October 2025].

 Retail Dive, 2025. The Rise of DTC Brands: ThirdLove, Savage X Fenty, and CUUP. Available at: https://www.retaildive.com/thirdlove-dtc-growth [Accessed 27 October 2025].

 Good Housekeeping, 2025. ThirdLove’s Comfort Revolution: Customer Reviews and Product Trials. Available at: https://www.goodhousekeeping.com/thirdlove-reviews [Accessed 27 October 2025].