What factor primarily influences the effectiveness of a color filler?

The primary factor that influences the effectiveness of a color filler is the hair's porosity. Porosity refers to the hair's ability to absorb moisture and products. Hair that is highly porous has gaps and holes in the cuticle layer, allowing it to take in color more readily. Consequently, when using a color filler, which is designed to equalize the hair's porosity and provide a more even base for coloring, the effectiveness can vary significantly based on how porous the hair is.

For instance, if the hair is very porous, it might absorb the filler quickly, allowing for more balanced color results. Conversely, if the hair is less porous, it might not take the filler evenly, resulting in uneven color application. Therefore, understanding and assessing the porosity of the hair is crucial for achieving the desired outcome when using color fillers.