But ask Sean Ashby, founder of one of Australia's most successful men's underwear labels, aussieBum, if he's surprised men are spending more money than ever before on their underwear and he'll probably laugh in your face.

"Surprised? Hell, no," Ashby says. "They're looking after their most valuable asset and you can't put a price on that."

He believes underwear sales have grown in line with the rise of the metrosexual.

Turnover has doubled each year since he started his business seven years ago.

"Men have become more fashion-conscious in recent years right down to their underwear.

"They are simply catching up with women; they want the same quality and choice that women have in their lingerie."

While unit sales of men's underwear have remained steady for several years, men are forking out significantly more on designer brands than ever before.

"The consumption rate in Australia has remained pretty solid, around seven pairs per man per year (women buy 10 pairs a year), but what has happened is men are spending much more per pair than they ever have," says Simon Winter, business manager for men's wear at Myer.

"Ten or 15 years ago, men were buying Seven Days in Rio and paying $7 for a pack of seven, and now they're spending $20 or, say, $40 or $50 if it's Calvin Klein, on one pair alone."

Some men are even spending up to $80 on designer underwear.

Diesel, for example, is currently selling a pair of trunks for Valentine's Day for $78.

"Over the past five years there has been significant sales growth in the luxury end of the market, in particular," Winter says. "Calvin Klein's sales (at Myer), for example, are about 30% up on what they were a couple of years ago. We have also seen a lot more players come into the market."

The new players include top-selling New York brands C-IN2 and 2(x)ist, which both offer bulge-boosting "contour pouch" briefs and fashion-forward lines in soy and bamboo, and Melbourne brand RistefskyMacheda.

Ashby believes the popularity of online shopping - at websites such as Belowthebelt.com.au - has also allowed men to become more adventurous with their underwear.

"In the past you'd go into a department store and the woman who served you looked like your grandmother and would give you that look of disapproval. Buying underwear in the privacy of your own home means you can buy whatever takes your fancy."

Ashby, who brought us the Wonderjock - the male version of the push-up bra - and jocks infused with ginseng and vitamin C, says the next big thing in the men's underwear market will be his Wonderbum briefs - designed to plump the behinds of "all the flat-arsed men out there".

"Everyone's becoming more and more body-conscious these days. Women have been getting this kind of help for years. But men need it, too."

Bum's the word

Best SELLERS

* aussieBum's Wonderjock, $21.95 - Over 500,000 pairs of the male equivalent of the Wonderbra have been sold since it was launched in 2006. It is also the best selling men's underwear brand at Selfridges in London.

* C-IN2's Contour Pouch Brief, $34.95 - Since its launch in 2006, the "profile-enhancing" Y-front has become the brand's bestseller in Australia.

* Calvin Klein's cotton elastane trunk and brief, from $32.95 - Myer's best-selling men's underwear.

WATCH OUT FOR

* Calvin Klein's new version of the Wonderjock - Body Boost - to be released next month.

* aussieBum's Wonderbum - a bottom-lifting brief due to land later this year.