Sonia Verma hated her wavy hair.

"I never knew which direction it would wave," she said. "When it was humid out, that was a bad thing."

But all that changed for Verma after she underwent thermal reconditioning, the new and improved hair-straightening treatment that's popping up in more salons nationwide.

"It's great. I do nothing to it now," Verma, a 30-something housewares buyer, said of her dark brown tresses. "I just comb and go." Verma added that several of her friends who live in cities from Chicago to New York have also received the treatment.

Also known as a Japanese perm due to its Japanese and Chinese roots, thermal reconditioning uses heat to change the shape of the hair. After the cuticle is broken down with chemicals, locks are ironed straight with a hot iron. A neutralization process then closes the cuticle, causing hair to stay straight.

The procedure has been around for several years, but recent advances have made it even more effective in getting all types of hair silky smooth.

"The products are getting better. Every day the technique is better," said Sammy Miyamoto of the Momotaro salon in New York City. Miyamoto has been performing the treatment for about four years, but says it's "really getting hot right now."

"It's becoming more and more popular," agreed Drew Broman, a stylist at New York's Maximus Spa and Salon, which began offering the treatment about six months ago.

Hairdressers all attribute the heightened demand for thermal reconditioning to its better-than-ever results -- but Mary Greenberg, editor of Celebrity Hairstyles magazine, said the stars are not without influence.

"Britney Spears, Jennifer Aniston, Sarah Michelle Gellar, Gwyneth Paltrow ... they all seem to want to wear their hair straight," Greenberg said.

Ty Holbrook, a stylist at the John Frieda salon in New York who performs the treatment for actress Julianne Moore (who guessed the redhead actually has wavy hair?) said clients who want the treatment come in clutching photos of stars like Moore, Cameron Diaz and Tyra Banks.

But why is Hollywood flattening out? Greenberg said many people perceive straight hair to be more polished, sophisticated and professional (the hair expert added that she herself has thick, curly hair and thinks it's a lot of fun.)

Celeb-glamorous hair also doesn't come cheap. Good deals can be found at Asian shops such as Momotaro, where the treatment runs about $325. But in fancier salons like John Frieda, the procedure can cost $600 to $1,000.

Becoming straight-laced is also time-consuming. The treatment takes four to six hours, depending on hair length and texture. Retouches are also necessary every six to eight months, as hair grows back the way nature intended.

But some say that for women who spend hours each week blow-drying their hair into submission and dodging raindrops like bullets, thermal reconditioning is worth the time and money.

"It is hard to sit still for five hours, but I would definitely get it done again," Verma said. "It was my saving grace."