et fashion decree tempestuous waves as the perfect complement to this season's haute bohemian look. Simona Liberman isn't buying it. Ms. Liberman, a New York cosmetics industry publicist, was reminiscing about the rigors she endured to tame her locks. "I used to be one of those people with the round, bristled brushes, always pulling and pulling and blasting away with a dryer," she said with a groan. "If it rained, I didn't go out."

This month, however, Ms. Liberman, 27, sat for several hours — and parted with hundreds of dollars — at Gil Ferrer, a New York hair salon, where she received a new high-tech straightening, a hot iron and chemical retexturing that left her undulant shoulder-length hair flat and smooth as a fresh-pressed sheet.

The procedure, a Japanese technology called thermal reconditioning, is primarily for well-heeled, fashion-fixated women, for whom a pin-straight, mirror-shiny mane is the ultimate in sexiness and chic. The process, which is marketed mainly to Asian and Caucasian women, involves coating the hair with a glycolic acid derivative and ironing it in sections an eighth of an inch thick. Labor intensive and time consuming, it requires the forbearance of a monk. But because it can leave all but the frizziest hair poker- straight for months — or as long as it takes new growth to appear — for some, it promises to render the salon blow-dry all but obsolete.

To Ms. Liberman and others who seek the treatment despite prices from about $300 to $700 or more, thermal reconditioning is cause for rejoicing. "It is definitely transforming," said Tara Hennigan, an account executive at the Gartner Group, a Connecticut technology research company. "And unlike a new pair of shoes or a dress, the thrill of its novelty doesn't wear off."

Elizabeth Lamont, the beauty editor of Harper's Bazaar, had her hair reconditioned almost a year ago and is still pleased. "I've always wanted to be one of those wash-and-go girls, and now I am," she said.

Thermal reconditioning, which began making its way into American salons about a year ago, is gentler and more consistently effective than traditional hair-straightening treatments. At one time, chemical straighteners were formulated with lye, a corrosive that damages the scalp and the hair shaft. Over time, lye gave way to other chemicals, some made for home use. While kinder to the hair, they worked only if the hair was blown dry every time it was washed.

Not so with the Japanese treatment, which uses a weakened version of ammonium thyoglycolate, followed by neutralization, drying and heating with a 180-degree straightening iron to break down the bonds of the hair and form a straight structure. The treatment, which leaves the hair limp, cannot be undone.

Because thermal reconditioning is still new to this country, no comprehensive sales figures are available. But as the latest advance in a hair- relaxers market estimated at a billion dollars a year, thermal reconditioning is expected to grow exponentially in the next months.

"Our business is increasing and increasing," said Yong Chong, the vice president of Shimbi in New York, a distributor of the Japanese chemical relaxers used in thermal reconditioning. Last year, the company sent its products to about 15 salons nationwide. This year, she said, it is shipping to 60 salons.

"Women do like this treatment," said Gil Ferrer, the hair stylist, who charges about $500 for it. "It gives some of them a younger look. But mostly, this is about fashion."

Margie Melaniphy, the editor of Salon News, a trade weekly, said the look cuts across ethnic background. "It's a very big trend and has been for a few years now," she said.

Straight hair has been overwhelmingly endorsed by fashion editors and celebrities. Gwyneth Paltrow is quoted in the March issue of Vogue as saying: "Straightening my hair is big for me in terms of feeling confident. If I have frizzy big hair, I feel like I have zero sex appeal."

Other poster girls for the look include Jennifer Aniston, Penélope Cruz, the pop star Brandy and the rhythm and blues singer Mary K. Blige. Even curly-headed Chelsea Clinton has gone for straight hair, which she showed off at this year's Milan and Paris fashion shows. And Carine Roitfeld, the editor of French Vogue, has made dead-straight hair her signature. Ms. Roitfeld's tresses, which curtain half her face, have lately been copied on the runways.

While some salons and beauty editors insist that the look is eternal, Marianne LaFrance, a Yale psychologist, said, "Straight hair is a trend like any other." Last year, Dr. LaFrance studied how hair affects self- image and the perceptions of others. "At one time we all wanted hair like Farrah Fawcett," she said. "Now we want our hair straight. Fashion comes and goes."

Clarissa Lamont, a law student and the twin of Ms. Lamont of Harper's Bazaar, said she wants to keep her curls. "I like the flexibility," she said. "I don't want to be a slave to my blow-dryer."

The desire for straight hair emerged in the 1960's, an emblem of hippie freedom. At the same time, it was a sign of preppy nonchalance, like a twin set and pearls. In some circles, a flat glossy mane projects class. "It's that whole sort of look that goes with sun-streaked blondness," said Paul Wilmot, a New York fashion public relations consultant. Straight hair is often perceived as an "Anglo look, as entrenched a part of American culture as the debutante," Mr. Wilmot added.

That notion remains widespread. In Dr. LaFrance's study, participants viewed pictures of women in a variety of hair styles and rated them for intelligence, sexiness and social standing. "When we showed them a photo of a woman with long, straight, blond hair, she was almost always assumed to be more sexy and more affluent," Dr. LaFrance said.

This perception suggests why women pursue straight hair and with it the new thermal treatment, despite potentially damaging effects. Though thermal reconditioning is an improvement on more conventional relaxers, it tends to leave the hair brittle. Dr. Steven Victor, a New York dermatologist with an Upper East Side practice, allowed that chemical relaxers can be safe.

"But a problem arises when they are left in too long or too much is used," he said. "At that point, the hair will break."

Nor is it effective, stylists say, for African-American women or on hair that has been bleached or permed. Women with overprocessed hair are advised to keep their curls.

Some see the look as sexy. "Men like it," Ms. Lamont, the beauty editor, said. "Straight hair worn down with side-flipped bangs — you definitely get more looks." Straight hair can also confer authority. Lisa Lange, 26, a fitness trainer, has been blowing her hair taut since she was 13. "You're taken more seriously, perceived as more professional and more intimidating, though not in a bad way," she said.

Even in Dolly Parton country, where big fluffy hair has been the norm, the flat-pressed look has become a coveted alternative. "We are getting requests for our products from everywere, even middle-sized towns in Utah, Texas, Maryland and Florida," Ms. Chong of Shimbi said.

While lanky hair tends to be viewed as a positive attribute, it does have a downside. In the Yale study, the straight-haired woman was consistently perceived as self-absorbed, Dr. LaFrance said. No matter. Women continue to cultivate straight hair. Ms. Lamont, the editor, for one, plans to repeat the process the moment her hair starts to wave. "How else," she wondered, "am I going to keep that terrific New Yorker's sense of entitlement?"