What is hair porosity?

Hair porosity refers to the hair ability to absorb and retain moisture. It depends on the condition of the cuticle layer — the outer protective scales of the hair shaft. Low porosity hair has a tight, flat cuticle that resists moisture. High porosity hair has a raised or damaged cuticle that absorbs moisture quickly but loses it just as fast.

How do I test hair porosity?

The float test is the simplest method: place a clean, dry strand of hair in a glass of room-temperature water. Low porosity hair floats, medium sinks slowly, and high porosity sinks immediately. The slide test involves running fingers from tip to root — bumpy texture indicates higher porosity. Drying time also indicates porosity level.

How does porosity affect hair colouring?

Low porosity hair resists colour absorption and may need longer processing or heat to open the cuticle. High porosity hair grabs colour unevenly and rapidly, often going darker than intended at the porous ends. Using a protein filler before colouring high porosity hair evens out absorption for more consistent results.

Can hair porosity change over time?

Yes, porosity can change. Virgin hair typically has low to medium porosity. Chemical treatments, heat styling, sun exposure and mechanical damage all increase porosity over time. While you cannot restore damaged cuticle, protein treatments temporarily fill in gaps, and acidic rinses help smooth the cuticle layer.

CutCalcs

Porosity Calculator — Hair Porosity Assessment

Assess hair porosity level and get product and processing recommendations.

Float Test Result

Place clean dry strand in water

Slide Test Result

Slide fingers from tip to root

Drying Time

Chemical History

How We Calculate This

This calculator assesses hair porosity by scoring four diagnostic indicators and providing a combined porosity rating with tailored product and processing recommendations.

The scoring system

Each of four tests is scored 1-3 points (1 = low porosity indicator, 3 = high porosity indicator). The total score (4-12) determines the overall porosity level.

Score 4-5: Low porosity
Score 6-8: Medium (normal) porosity
Score 9-12: High porosity

Frequently Asked Questions

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Last updated: February 2026

All calculations are estimates. Always perform a strand test before chemical services.