While synthetic hair is about a fourth the cost of human hair, most celebs use human hair extensions, such as Great Lengths (Hilton and Nicole Richie's company of choice) to get the long hair nature hasn't blessed them with. Each strand is "pre-tipped" with a synthesized keratin protein that acts as a glue to bond the strands onto hair. Heat may be used to bond, or "melt" the glue, or some stylists use FastFusion technology, which uses air pressure to bond individual hairs in faster time.
Prices run anywhere from $10 for a single extension to $2,000 for a full head of not-your-own-yet-still-human hair. Visit www.hairuwear.com for a list of salons and to see before and after shots.
Don't want extensions glued to your own hair? Clip-ons made from human or synthetic hair (Ken and Jessica's line includes hair made from Vibralite fiber) let you flirt with a new look without committing to it. Popular brands include by Hair U Wear and Easihair.
Clip-ons are easier to use and don't require professional application. You simply slip them in just below the crown, while keeping top layers out of the way with clips. Because they are do-it-yourself, clip-ons are cheaper than the more permanent version. For an idea of prices or to buy now, check out Jessica and Ken's extensions here.