Which tool is commonly used to create curls in hair using heat?

The tool that is commonly used to create curls in hair using heat is a curling iron. Curling irons are specifically designed for the purpose of curling hair by applying heat to sections of hair wrapped around a cylindrical barrel. This allows the hair to take on the shape of the barrel, resulting in defined curls or waves.

Moreover, curling irons typically come in various barrel sizes, enabling stylists to create different styles of curls ranging from tight ringlets to loose waves, thus making it a versatile tool in hairstyling. The significance of heat in this process is that it alters the structure of the hair temporarily, allowing it to hold the desired curl shape once cooled.

In contrast, a flat iron is primarily used for straightening hair and can create waves or curls under certain techniques, but it is not specifically designed for curling. A drier is used mainly for drying hair and may not provide the curled effect using heat on its own. A round brush is often utilized in conjunction with a blow dryer to achieve volume and smoothness rather than curls. Therefore, the curling iron stands out as the most appropriate choice for creating curls with heat.