Chalk it up to the popularity of yoga pants and workout tanks.
As female shoppers purchase more athletic apparel, the rise of "athleisure" has already caused a subsequent spike in the popularity of athletic shoes. Now, the lifestyle shift appears to have another beneficiary: the sport bra.
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According to The NPD Group/Consumer Tracking Service, U.S. dollar sales of sport bras are on the rise, as revenues from the undergarment's traditional version are inversely taking a hit.
Just take a look at Hanesbrands' most recent earnings call. In the second quarter, the firm said sales in its innerwear division fell 1 percent, stemming from a decline in intimates. By contrast, revenues from its activewear division—albeit aided by the acquisition of Knights Apparel—increased 19 percent.
Speaking to the category as a whole, Hanesbrands' Chief Operating Officer Gerald Evans said intimates sales have declined at a high single-digit rate over the past year.
"Part of it is a trade-off from the athleisure trend, part of it is comfort," NPD's Marshal Cohen said. "The other part is the lack of innovation in traditional bras compared to that in the sport bra business."
Though NPD declined to provide specific growth numbers for the bra category, it did say that the sport version now accounts for 20 percent of the $6.3 billion market by dollars. And as that piece of the pie grows, both athletic brands and traditional lingerie stores are putting a greater focus on the segment.
Under Armour, which on its latest earnings call pointed to sport bras as one driver of growth in its women's business, recently launched a new chapter in its female-focused ad campaign around the new Armour Bra Collection.
Similarly, Nike said during its June financial report that "key apparel styles such as the Nike Pro Bra Collection" are "resonating strongly with consumers and creating excitement in the marketplace." That brand, whose women's business last year grew 20 percent on a constant-currency basis to nearly $6 billion, is also upping the number of stores that offer bra-fitting services.
Dick's Sporting Goods has created a multi-branded bra "destination" in its stores, adding that it expects the category to be a key part of its new women's-only Chelsea Collective Stores. Those locations will also feature professional bra fitters.
And Victoria's Secret, which has built its reputation more on push-up bras than push-ups, said that its sport business "is exceeding our expectation, especially as we continue to focus on the bra category."
Unlike HanesBrands, however, the L Brands-owned company is also experiencing strength in its core bra and panty business.
"We believe the revamped Very Sexy and Body by Victoria collections likely aided results," Guggenheim Securities analyst Howard Tubin wrote in a note to investors following the company's July sales results.
That vibrancy, however, has not been felt industrywide. Troubles at the more risqué Frederick's of Hollywood, for example, pushed the brand to file Chapter 11 for the second time in April. Frederick's has since been purchased by Authentic Brands Group, which said it will expand the brand's presence into beauty, fragrance and personal care.
According to The NPD Group, women's activewear sales rose 8 percent on a dollar basis last year. Women's athletic footwear sales have experienced similar growth, rising 8 percent through the first six months of this year.
The overall underwear market was worth $15.7 billion last year, according to Euromonitor data, representing an increase of 0.7 percent. The firm is forecasting a similar growth rate for 2015.