Men's underwear sizes are getting smaller while the industry grows, but boxers still remain the most popular style for men in the U.S.

According to VOA News, growth in the U.S. men's clothing market has surpassed that of the women in the past three years. The men's underwear 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.

In particular, slimmer styles of men's underwear grew 11 percent over the past year. However, according to VOA News, boxers still remain the most popular underwear size for American men (though it declined by 14%), followed closely by boxer-briefs (40%) and briefs (23%).

As tighter-fitting jeans and pants are coming back into style for men, slimmer underwear is following suit.

"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 Marshal Cohen, chief retail analyst for The NPD Group. "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."

According to VOA News, in 1975, only 25 percent of all men's underwear was purchased by men, the rest likely bought by a girlfriend, wife, 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.

"The undergarment business is not just for women anymore and that's really what this is all about," Cohen added. "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."