The rise of “athleisure’’ apparel and the increasing demand for varied wardrobes are changing the way women shop for undergarments, specifically bras.

That’s the conclusion of a 2015 analysis of the “bra journey’’ by the market research firm NPD Group.

Comparing the shopping patterns of millennials to previous generations, the NPD report says that changing definitions of comfort — underlined by the popularity of sweat shirt-yoga pant ensembles — have paved the way for new norms when it comes to selecting and purchasing bras.

“All bra consumers seek comfort, but differences in their bra introduction and life stage timeline have impacted how Millennials and non-Millennials arrive at comfort throughout their lives,’’ said Marshal Cohen, NPD’s chief analyst, in a statement.

“The comfort and wearability of the athleisure apparel trend, that is embedded in the Millennial style vocabulary, will compel them to seek the same type of comfort and ease of movement throughout their bra journey.’’

Among young women, sports bras are the most popular style, followed by push-up bras and full-coverage types. That marks a shift from non-millennials’s top three styles. Among those women, full-coverage is the most popular, followed by wire-free and then sports bras. In other words: activewear and uplift are in for millennials, while cleavage-concealing, ultra-supportive styles are out.

Sports bras made up 20 percent of bra sales, according to CNBC last August. The bra market is a $6.3 billion category.

Millennials also seem distinct from previous generations of women in that they increasingly cite wearing multiple bra styles, while noting “newness’’ and “change in size’’ as top reasons to pick up new intimates. Meanwhile, brand names are far less important to the new wave of shoppers, according to the NPD report. Only 58 percent of millennials rated “carries the brand I want’’ as an extremely important qualifier when deciding where to shop, versus 77 percent of non-millennials.

Lest baby boomers and GenXers start to panic, it should be noted that there’s still some common ground across all age demos. In general, 80?percent of bra purchases are planned and primarily instigated out of a need to replace the garments. And more than 50 percent of women buy three or more bras at once, trying them on at home and not returning them.

“The intimate apparel industry needs to embrace the differences while finding the common currency among today’s bra shoppers,’’ Cohen said. “Although their definitions of comfort may differ, Millennials and non-Millennials will buy more than one bra when they find the one that suits their lifestyle.’’

Isaac Feldberg can be reached at isaac.feldberg@globe.com.