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Hair Porosity and Why It Matters

Porosity describes how easily water gets into and out of your hair, and it is more useful for choosing products than curl pattern is. It is also the thing most often assessed with a test that does not work, so it is worth knowing both what porosity is and how to actually tell where yours sits.

The float test is unreliable

Dropping a shed hair in a glass of water and watching whether it sinks is the test everyone knows. It does not tell you much. Product residue makes hair float regardless of porosity, a strand's own surface tension can hold it up for several minutes, and whether it sinks depends heavily on how it entered the water. People get different results from the same head of hair on the same day. Treat it as entertainment rather than information.

What actually tells you

Two everyday observations. First, how long the hair takes to get properly wet in the shower: hair that resists water and takes a while to saturate is low porosity, and hair that soaks instantly is high porosity. Second, how long it takes to dry: low porosity hair takes a long time, since the water that got in struggles to get out, while high porosity hair dries quickly. Add a third if you like: whether products sit on top of the hair or disappear into it.

Low porosity

The cuticle lies flat and tight. Water and product struggle to get in, so hair takes ages to wet and ages to dry, and products build up on the surface rather than absorbing. What helps: lighter products, applied to very wet hair, with warmth. Heat during deep conditioning matters more for low porosity hair than for anyone else. Heavy butters and oils mostly sit on top and cause buildup, so clarify regularly.

High porosity

The cuticle is raised or damaged, from processing, heat, or naturally. Water goes in fast and leaves fast, so hair wets instantly, dries quickly and feels dry again within hours. What helps: heavier creams and sealing oils to slow the water leaving, layering products rather than relying on one, and protein periodically, since raised cuticles usually mean gaps in the structure.

Porosity changes

It is not fixed. Color, bleach, relaxer, heat and time all raise porosity, and it can differ across your head, with the ends more porous than the roots simply because they are older. This is why the ends of long hair often want a heavier product than the roots do.