Porosity measures the hair's ability to absorb and retain moisture and color. It depends on the cuticle — the outer protective layer of the hair formed by overlapping scales.
Hair with a tightly closed cuticle (low porosity) resists dye penetration. The color molecule struggles to enter, which can result in lighter-than-expected color or slower processing. Conversely, hair with an open cuticle (high porosity) absorbs quickly but loses color just as fast.
The three porosity levels
Low porosity: Tightly closed cuticle. Hair repels water and products. Typical of virgin hair, thick hair, or genetically resistant hair. For coloring: needs more processing time, may benefit from gentle heat, and initial color may appear slower but lasts longer.
Medium porosity: Balanced cuticle state. Absorbs and retains well. This is the ideal state. Manufacturer processing times work as a reliable reference.
High porosity: Open or damaged cuticle. Common in repeatedly bleached hair, heat-damaged hair, or hair exposed to chlorine/sun. Absorbs color in seconds but loses it in a few washes. Requires adjustments: lower developer volume, higher proportion of natural base (.0/N) in the formula, and pre-treatments to equalize porosity before the service.
Porosity and color formula
Experienced colorists adjust the formula based on porosity:
- Developer: Lower volume for high porosity (6vol instead of 20vol for deposit). Higher volume for low porosity when penetration is needed.
- Time: Reduce 5-10 minutes for high porosity. Add time or heat for low porosity.
- Formula: Add natural base (.0/N tone) for high porosity to anchor color. Use pure tones for low porosity since retention is good.
- Pre-treatment: For uneven high porosity, apply an equalization treatment (protein filler) before color to homogenize absorption.