What a Diffuser Is
A diffuser is an attachment applied to the end of a hair dryer. It is generally rounded and features several long, rod-like pieces. A diffuser is most often used when drying curly or wavy hair because of the special properties this hair type has. A hair diffuser also may be used if you have heat-damaged hair because a diffuser is generally considered to be less damaging to the hair. When a diffuser is attached to the hair dryer and then turns on, the air circulates or diffuses around the curl, instead of being blown straight onto it.
Curly Hair Properties
Curly hair dries in the opposite manner that straight hair does. For example, when wet, curly hair tends to be straight in appearance. It then uses the moisture from the water to absorb into the hair and contract to create curls. Conversely, when straight hair dries, it must shed moisture to be straight. This is why using a diffuser works for those with frizzy or curly hair. If those with this hair type used a regular hair dryer with no nozzle attachment, the hair has a tendency to become frizzy in appearance because the hair was not able to retain fully the moisture it needs to curl fully. Also, extreme amounts of heat applied directly to the hair can break down the chemical bonds, causing the hair to relax. A diffuser is often used on a low heat setting, which allows curly hair to retain its chemical bonds, preventing the hair from relaxing and appearing frizzy.
Applying a Diffuser
When a diffuser is applied to wet hair, the air circulates around the curl. This allows it to mimic the properties of air drying curly hair, which results in more clearly defined curls. Using a diffuser often takes a longer time to dry the hair than using a standard hair dryer might. However, the hair appears softer and less frizzy. Diffusers often are helpful in adding volume to flat hair. The diffuser's rods help to separate the hair better, which gives it an added lift and adds volume for a fuller effect. Drying the hair upside down while using the diffuser also will help to separate the roots of the hair more for an added boost.