Which styling product adds volume to fine hair?

Mousse is specifically designed to add volume and body to fine hair, making it the ideal choice for this purpose. It contains lightweight polymers that can expand when applied to the hair and whipped during styling, resulting in increased volume without weighing the hair down. This is particularly beneficial for fine hair, which often lacks fullness and can be easily flattened by heavier products.

In contrast, hair gel primarily provides hold and structure but can make fine hair appear stiff and may weigh it down if too much is used. Hair serum is typically used to add shine, reduce frizz, and hydrate the hair, but it does not contribute to volume and can often make fine hair appear even sleeker, which might not enhance the desired fullness. Hair spray serves as a finishing product that can help to hold a style in place but does not particularly add volume at the styling stage. Thus, mousse is the most effective option for promoting volume in fine hair.