If you've ever noticed a short-haired star change her look to long locks relatively quickly, then you've seen hair extensions. A few strategically placed strands can mimic highlights, or larger chunks can make hair appear longer and fuller. In Britney Spears' case, they can cover up a bad haircut. But there are a few things to know before you start the process. First, it's not cheap. An application of human hair over the entire head can run you $2,000 or more. Then there's maintenance as your natural hair grows out and products made specifically for treating extensions. They last several months if maintained properly and if applied by a professional stylist. You can opt for synthetic hair or actual human hair, which blends with natural hair better, is much easier to style and can be curled, blown dry or heat styled in any other way. Synthetic hair typically melts when heat is applied, so it's best only for straight styles. A stylist should select extensions that match your own hair's weight and texture to create the best match.