Choose your brush wisely! According to Vaccaro, brushes that are too big (think 3-inch diameter and above) will result in a superstraight outcome, because the hair won't wrap around the ends enough for a curl. On the contrary, smaller brushes (1 1/2 inches to 2 1/2 inches) will add waves to the style because the hair can wrap around the brush tightly, multiple times, while being held against the dryer.
"Bigger brushes are also more efficient, shortening the blowout time because more hair is lifted against the heat at a time," Vaccaro added. However, as a general rule, a 2-inch-diameter brush is universally best for at-home blowouts because it's known to give a similar straightened effect that a 3-inch brush can deliver, without having to sacrifice on the volume or movement that a 1 1/2-inch brush can create.