Caring for hair by porosity

The definition and biology of porosity are covered in hair porosity. This page covers how to adjust products and routine, and how much of that advice is evidence-based. The short answer is that little of the low, normal and high porosity routine advice has been tested in people.

Key takeaways

• In science, porosity means measurable pore volume and surface area inside the fibre, measured by gas sorption, not by a glass of water. Oxidative bleaching raises hair surface area (nearly tripling it in the first minute in one experiment) while UV damage follows a different pattern, so porosity is not one simple dial. Hessefort 2008
• Washing itself raises porosity. Surfactants diffuse in, dissolve protein and enlarge pores. A coconut-oil treatment reduced that increase in a study by a coconut-oil manufacturer (industry-funded, lab only). Kaushik 2022
• The float test is a weak home check. The New York Society of Cosmetic Chemists calls float and spray tests qualitative methods with "limitations", and we found no peer-reviewed validation.
• Perceived moisture is not measured moisture. The same society notes that "perceived hair moisturization does not correlate with actual hair moisture content".
• A practical proxy is behaviour. Hair that is slow to wet and stays product-coated is often called low porosity. Hair that wets instantly, dries fast, frizzes and tangles is often called high porosity. Heat, bleach, colour and relaxers raise porosity along the length, so one head usually has several.
• Matching routine to porosity is reasoned, not proven: lightweight water-based products and gentle warmth for low porosity, richer conditioner, sealing and acid-balanced products for high porosity.

The science

Porosity at the fibre level reflects cuticle integrity, loss of the lipid layer and, in the cortex, loss of matrix protein. Oxidative treatments break down structure so pores form and later merge into larger ones. In Hessefort's experiment, surface area rose, then dropped after about 10 minutes of bleaching. Hessefort 2008 Bleached and chemically treated hair is more porous, swells more with water and has a more negative surface charge, so conditioners deposit more. Gavazzoni Dias 2015; Labarre 2023

What it means for your hair

Curl pattern interacts with this. Coils (3C-4C) are drier along the shaft and often need richer products whatever the porosity (reasoned, not tested here).

Myths and facts

• Myth: "Low porosity hair can't absorb moisture." Uptake is slower, not impossible, and buildup is often the real culprit.
• Myth: "Oils moisturise high porosity hair." Oils are not water. Coconut oil reduced water-related protein loss in lab studies, which is protection rather than hydration. Kaushik 2022
• Myth: "The float test tells you your porosity." It is unvalidated, and sebum, product residue and water conditions all change the result.

Bottom line

Judge by what your hair does (wetting time, drying time, frizz, tangling, colour fade) rather than a floating strand. Expect ends to behave differently from roots and condition the ends more. If everything feels coated, clarify before adding more product. Reduce the cause where you can, because heat and bleach drive porosity up and cannot be undone cosmetically (see bond builders).