If you've ever wondered how the heck it's possible that every Hollywood starlet always has amazing hair, it's not just because they're genetically blessed or have a stylist on-call at all times (although that obviously doesn't hurt). The secret behind the celebs' luscious locks -- and all those stunning styles you see on Insta -- is clip-in hair extensions. Trust us, even if they say they're not wearing them, they are. So if you feel like your locks are lacking, extensions offer the perfect solution. Clip 'em in for a night, take them out the next. Voila: Instant versatility.

Ahead, the ultimate guide to clip-in hair extensions, with everything you need to know about choosing the right ones, putting them in, and using them to create stunning styles. We see some seriously good hair days in your future.

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Unlike changing up your look with a new cut or color, the biggest benefit of clip-in extensions is that they're temporary and require no commitment, says Riawna Capri, co-owner of 901 Salon in West Hollywood, CA, and stylist to stars like Julianne Hough. And it's not just about adding length; hair extensions can be used to incorporate more fullness and volume, too, totally transforming even the most basic styles.

Then there's also the matter of color: "Sometimes you create a beautiful style on dark hair and the detail gets lost. Adding just a few clip-in extensions that are slightly lighter can instantly give that style the dimension it needs," explains Capri. Not to mention that if you want to experiment with trendy hair hues (unicorn hair, anyone?) clip-ins are the best way to temporarily switch up your shade.

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Not all types of extensions are created equal, and picking the best hair extensions is half the battle when it comes to ensuring the end result looks completely natural and believable (because no one wants hair extensions that remind you of Britney Spears circa 2006). Above all, make sure you choose a product that's made of 100 percent human hair. "Simply put, synthetic hair looks fake because it is fake. It's shinier than real hair, which is what makes it stand out," explains celebrity hairstylist Ashley Rubell, who works with Lena Dunham.

The majority of high-end hair extensions out there are made with what's known as Remy hair, human hair that's been sifted through so that all the strands fall in the same direction to help eliminate tangles, notes Rubell. Some of the best clip-in hair extensions to try: Jen Atkin by Beauty Works Invisi-Clip-In, $371.99, Glam Seamless Clip-In Extensions, $279.99, and Barefoot Blonde Hair, $194.99.

Picking the right color is also essential: "You can easily spot bad hair extensions when the color doesn't match," says Capri, who advises choosing a hue that matches your color exactly, as well as a few others. For example, if you're blonde with highlights, choose extensions that match both your base color and the lightest pieces. "Most people, even those who have never dyed their hair, have more than one color or tone in it, so the clip-ins should also be dimensional," adds Capri.

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As a general rule, Capri recommends always keeping clip-ins at least one inch away from your hairline. "The hairs here are the thinnest and most fragile, so you don't want to put any extra tension on them," she explains. "Keeping the extensions away from the hairline will also prevent any telltale pieces from peeking out." Also important: Avoid placing hair extensions in straight lines. "Follow the curvature of you head, picturing a 'U' shape. When putting them in on the sides, tilt them on a slight angle," suggests Rubell. This helps the pieces fall and blend better with the rest of your hair, ultimately making for a much more natural and seamless effect. After all, you want the final style to be the thing that people notice, not the extensions themselves, Rubell adds.

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