The American male has long been judged a fashion dud.

The uniform of the Silicon Valley guy, after all, is a hoodie and T-shirt. Khakis and golf shirts show up on days other than casual Fridays.

But millennial guys in their 20s and 30s are transforming the menswear business, inspired by well-dressed male celebrities and TV shows such as “Mad Men” that celebrate bygone eras when pocket squares were de rigueur.

“Men are more in tune and more interested in looking good and sharp,” said Will McKittrick, an industry analyst at IBISWorld. “The younger generation is entering the workforce and beginning to spend a lot more on fashionable clothing.”

Although women’s clothing still sells more, menswear has been expanding at a faster clip.

Over the last two years, men’s retail sales jumped 4.1% to $101.8 billion, eclipsing the 2.8% rise to $150.1 billion on the female side, according to research firm Euromonitor. By 2017, menswear is expected to climb 8.3% to $110.3 billion, compared with 4.2% to $156.5 billion in women’s.

Retailers facing a clogged market for the ladies are now sprinting to outfit the modern man.

Luxury brands including Prada and Hermes have opened boutiques just for men. Nordstrom dropped $350 million in August to buy online men’s styling service Trunk Club.

Southern California has become a major hub for emerging menswear brands that deliver a distinct spin on men’s fashions.

The region’s affinity for street wear and its deep manufacturing base have nurtured dozens of budding designers for guys. When GQ magazine, considered a style bible by fashionable fellows, named its best new menswear designers of 2014, two out of the four were based in Los Angeles.

The surge in men’s apparel has even spawned its own lingo.

Analysts have dubbed the demographic driving the growth as the Henry (high earner, not rich yet) and the Yummy (young, urban male).

The looks that Henrys and Yummies are adopting to replace saggy jeans and T-shirts with ironic sayings? Among the archetypes: the modern gent (mixes suits with patterns and textures), the urban dapper dude (wears expensive street wear such as leather sweatpants), the upscale casual guy (goes for high-quality, high-cost basics) and the lumbersexual (a twist on the term “metrosexual” referring to guys in plaid shirts with well-groomed beards).

Menswear labels are not only delivering fresh takes on the male look, they’re also rethinking how men want to shop.

At J. Crew, which has opened a dozen male-only shops in the last few years, cutting down on the number of decisions men have to make is a key reason those boutiques have worked, said Frank Muytjens, head of menswear design. Guys trust that J. Crew has done all the “weeding” to offer the best styles, he said.

“Our guy doesn’t have time to think anymore. We did that for him,” Muytjens said, adding that J. Crew has come a long way since he started there 11 years ago. “We didn’t have separate men’s stores,” he recalled, “and I always felt that guys had to scale walls to get to their departments.”