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If you want larger curls, or if you mostly just want to add volume, opt for large rollers, like a 1–2 in (2.5–5.1 cm) diameter. If you’d prefer tighter curls, use small or medium rollers, which typically range from 1⁄4–1⁄2 in (0.64–1.27 cm) in diameter.  Rod-shaped curlers are great for creating spiral curls or defining natural curls. They're also perfect for curling short hair, since they tend to have a smaller diameter. If you don’t have rollers, you can cut strips out of an old T-shirt, instead. Make the strips the same width that you want your curls to be, and a little longer than the length of your hair. Foam rollers might get damaged if you put them into wet hair, so make sure to use a roller that’s designed to be used while your hair is damp. Also, look for a soft roller, like one made from rubber, satin, or silicone, if you’re planning to sleep with the rollers in. Wash and condition your hair, or just spritz it with water from a spray bottle. If you’re starting with wet hair, gently blot your hair with a soft towel until it’s damp. The curls will hold better if you start with damp hair, but if it’s too wet, it might not dry completely once you put in the rollers. Do not apply serum or leave-in conditioner to your hair, as the curls may not set. By following a pattern when you’re rolling your hair, you’ll end up with a more symmetrical style, and it will be easier to keep the sections separate. Start by rolling the top section of your hair, or the mohawk area, all the way back to your crown. When you’re finished, you should have a neat row of horizontal rollers all the way along the top of your head. This will give you plenty of volume at your roots. Once you’ve rolled the front section, take another section of hair near one of your ears. This time, hold the hair straight out from your head horizontally, and place the roller vertically at the end of your hair. Roll the hair all the way to your scalp and secure it again, then continue for the hair on both sides of your head.  Roll your hair under for curls that curve toward your neck, or roll it up for curls that bounce outward. You can arrange the rollers at the back of your head horizontally or vertically, depending on the look you’re going for. Using horizontal rollers will give you more of a voluminous curl, while putting in your rollers vertically will result in more of a spiral curl. Since you’re not using heat, it will take several hours for the curls to set, so plan to leave the rollers in for at least 4 hours, although overnight is better. If you want your hair to dry faster without adding any heat, use a hair dryer set to its coolest temperature. Hide the rollers by wrapping your head in a silk scarf if you need to go somewhere before your curls are set. Once your hair is completely dry, take the clips out of the rollers, untie the T-shirt strips, or remove the bobby pins from your hair. Do this gently, especially if you want tighter curls.  For loose curls or big waves, gently run a wide-toothed comb through your hair. You can also run your fingers through your curls to fan them out, but do not brush them. Set the look with a little hairspray if you'd like.

Summary:
Choose wet-set rollers that are a little smaller than the curls you want. Dampen your hair. Continue rolling the top section of your hair. Roll the sides and back of your hair to finish. Leave the rollers in place until your hair is dry. Remove the rollers and loosen your hair.