Chris Rock's new documentary about African-American tonsure is haunted by the spirits of both Michael Moore and Michael Jackson. St. Michael of the Pseudo-Documentary inspires Rock's genial comic approach, while St. Michael of the Ethnic Assimilation hovers over the movie's subject of black hair straightening. Like recent filmic exposés of fashion or food, Good Hair conveys the dizzying dimensions of a culturewide addiction. The hi-def video imagery is rather too clinical on the big screen: Rock stirs a 7,000-pound vat of hair relaxer, caustic white sodium hydroxide dubbed by its users "the creamy crack." He also journeys to the source of black hair extensions—India—discovering a supply-side far holier than the demand. (The hair donors are making a religious offering.) Rock notes the irony, but doesn't compare it with that of Alabama hairdresser Kevin Kirk, who demands his fashion models not only pray for the Lord's blessing, but fast as well.

Of course, Rock interviews a cavalcade of black celebrities, who cannot imagine how their thousand-dollar extensions are affordable to "the other half" of black America. That lack of imagination, from the very role models who spur demand, limits the film's insight into why this particular vanity industry commands $9 billion a year. When rapper Ice-T and Rev. Al Sharpton, both sporting slicked-back locks, insist on their manly right to touch a lady's extensions, one senses the complacency of the rich and famous. Is the Reverend really, as he puts it, "combing his exploitation every morning"? Why doesn't he stop? Rock plays nice and doesn't ask such questions. And surely he could have found more representatives of the female 'fro.

Many of the film's highlights can be found in its 2 1/2-minute trailer, with the exception of hairdresser Jason Griggers, a swishy white boy breaking his own strange "color barrier" to join the elite straighteners of black women's hair. He also submits to the Caucasian's painful vanity treatment of choice: Botox injections! Rosy with post-op swelling, this handsome blond Georgian drawls, "I don't feel as beautiful as I had anticipated." St. Michael himself never confessed as much. It's a rare hint of regret for a film that ultimately gets swept up in that tawdry beauty contest. Like its trendy namesake, Good Hair sacrifices volume for sheen. PG-13.

Good Hair

opens Friday at Lloyd Mall and Eastport.