These brushes are available in small, medium, large and jumbo-sized barrels. When used with the heat of a blow dryer, the smaller round brushes act like rollers to create curl and movement. The larger round brushes smooth tresses and add body.
In both cases, the brush works because the metal core heats up, shaping the hair from the inside out. When you use your cool-shot feature (on your blow dryer), the metal core cools off. The length of your hair and the desired finished look determine which size brush to use.