Sales of slimmer-silhouetted underwear bottoms for men grew 11 percent over last year, while looser fitting styles experienced declines. (AP Photo)

Sales of slimmer-silhouetted underwear bottoms for men grew 11 percent over last year, while looser fitting styles experienced declines. (AP Photo)

American men are paying more attention than ever to what they wear and a big part of that growth is centered on what most people they encounter don’t see: underwear bottoms.

Over the past three years, growth in the U.S. men’s clothing market has surpassed that of the women.

The men’s underwear bottoms market reached $2.7 billion, a significant chunk of the overall $10 billion men’s clothing industry, and grew 3 percent from October 2012 to September 2014, according to The NPD Group.

“The undergarment business is not just for women anymore and that’s really what this is all about,” said Marshal Cohen, chief retail analyst for The NPD Group. “This is all about being able to make a statement, just as women have for centuries with their undergarments, men are now in the same place. Equality isn’t just about women gaining on men, this is about men finally figuring out they too can look fashionable even from the inside out.”

British soccer player and model David Beckham promotes his men's underwear line on Feb. 1, 2014, in New York. (AP Photo)O

British soccer player and model David Beckham promotes his men’s underwear line on Feb. 1, 2014, in New York. (AP Photo)O

But even as the underwear market for men expands, it’s also shrinking. After years of the saggy pants look, which showcased the wearer’s boxers, men are moving toward a more streamlined look, both inside and out.

“We’re seeing a movement away from the wear-your-pants-down-to-your-knees look and that’s also changing the way in which guys are looking at what they’re wearing, so they’re starting to wear slimmer, trimmer undergarments,” said Cohen. “And they’re also saying, ‘Wait a minute, if I’m going to spend so much time working out, or staying time, I want to show that off, too.’ So they’re not going for the baggy look.”

Men’s slimmer bottoms grew 11 percent over the past year, but boxers still remain the most popular silhouette for American men, followed closely by briefs and boxer-briefs. Part of the reason for the underwear boom is because more guys than ever are buying their own undergarments.

Back in 1975, only 25 percent of all men’s underwear was purchased by men; the rest was bought for them, probably by a wife, girlfriend or mother. These days, 75 percent of all underwear is bought by men.

“And what that basically means is that guys are now buying their own underwear and they’re no longer just accepting what was bought for them, but they are actually making choices,” Cohen said.

Their choices are more varied than ever. Growth in active underwear is helping to drive the market. Men are not just wearing active underwear while exercising, many are putting them on every day, in the same way many people have taken to wearing running shoes every day for comfort.

And while older men are more set in their ways — they’ve always worn briefs and few have shifted from that — the younger consumer — those under 40 — is building his wardrobe with a combination of styles. Which means the boxer’s reign as the king of men’s underwear, could soon be coming to an end.