You follow the same haircare advice as someone whose hair looks great. You use similar products. You try the same routine. Your hair still looks wrong: flat or frizzy, dry or greasy, never quite the way it’s supposed to. Porosity is often the explanation that’s missing from these conversations.
Hair porosity is not a trend. It’s a genuine structural characteristic of hair that affects how it absorbs and retains moisture, and it largely determines which products and techniques work for a given person’s hair.
What hair porosity actually means
Hair porosity refers to how easily the hair shaft absorbs and retains moisture and other substances. It’s determined primarily by the condition and structure of the cuticle, the outermost layer of the hair shaft made up of overlapping scale-like cells.
When cuticle cells lie flat and tight against each other, they limit what enters and exits the hair shaft. This is low porosity. When cuticle cells are raised, lifted, or damaged, the hair absorbs moisture more easily but also loses it more easily. This is high porosity. Normal or medium porosity sits between the two extremes.
Porosity is partly genetic (fine hair tends to have lower porosity than coarse hair) and partly acquired through damage. Chemical processing (colouring, bleaching, relaxing, perming), heat styling, UV exposure, and mechanical damage all raise the cuticle and increase porosity. This is why naturally virgin hair often behaves differently from hair that’s been chemically processed over years.
How to determine your hair porosity
The float test is the most commonly cited method: drop a clean strand of hair into a glass of water and watch what happens. Low porosity hair floats, medium porosity hair sinks slowly, and high porosity hair sinks quickly. This test is a rough guide but not perfectly reliable, as product buildup and other factors can affect the result.
More practically, notice how your hair behaves:
- Does water bead up on your hair when you wet it, or does it absorb immediately? Beading suggests low porosity; immediate absorption suggests higher porosity.
- Does your hair take a long time to get fully saturated in the shower? This is low porosity.
- Does your hair dry very quickly after washing? High porosity hair loses moisture faster, so it also dries faster.
- Do products sit on top of your hair rather than being absorbed? Low porosity.
- Does your hair get frizzy quickly in humidity? High porosity.
- Does your colour fade unusually fast after dyeing? High porosity allows colour molecules to enter and escape more easily.
Low porosity hair: what it needs
Low porosity hair is often healthy but stubborn about moisture. Products sit on top rather than penetrating, causing buildup without actually hydrating the hair. People with low porosity hair often complain that nothing seems to absorb and their hair looks dull despite using moisturising products.
For low porosity hair, heat is the key to opening the cuticle temporarily and allowing moisture and conditioning ingredients to penetrate. Deep conditioning with heat, using a heated cap, sitting under a hooded dryer, or even the steam from a shower, makes a significant difference to how well conditioner penetrates.
Lightweight, water-based products generally work better than heavy butters and oils for low porosity hair. The molecule size matters too: smaller molecules like water-soluble silicones and certain humectants (glycerin, aloe) penetrate more easily than large film-forming ingredients.
Protein treatments are often not necessary for low porosity hair and can cause buildup. If the hair structure is intact (which it often is with low porosity hair, since low porosity is frequently associated with undamaged cuticles), adding protein can make the hair feel stiff.
High porosity hair: what it needs
High porosity hair is the opposite problem: it absorbs moisture quickly but loses it just as quickly. This leads to the characteristic dryness and frizz of high porosity hair, which is common in naturally coily or curly hair types as well as in chemically processed hair.
For high porosity hair, the goal is to slow down moisture loss. This means using occlusive and sealing products, particularly oils and butters, on top of lighter moisturising layers to create a barrier that traps moisture. The “LOC” or “LCO” methods popular in curly hair communities (liquid, oil, cream in some order) are designed specifically for high porosity hair that needs layered sealing.
Protein treatments genuinely help high porosity hair because they temporarily fill the gaps in the raised cuticle, reducing moisture loss and improving strength. Regular protein conditioning, not every wash but perhaps weekly or fortnightly, can significantly improve the feel and behaviour of high porosity hair.
Avoiding hot water, minimising heat styling, and using a microfibre towel or a soft cotton t-shirt to dry (rather than a regular towel that causes friction and further cuticle lifting) all help maintain the porosity at a lower level.
A well-formulated hair serum with lightweight oils can help seal the cuticle of high porosity hair, reducing frizz and slowing moisture loss without weighing hair down. The key is using it on damp rather than dry hair so it seals in moisture rather than just coating dry hair.
Medium porosity hair: the easier case
Medium porosity hair is the least demanding. It absorbs moisture reasonably well, holds it reasonably well, and responds well to most standard hair products. If you have medium porosity hair, most generic haircare advice will work for you without needing to adapt much.
The main thing to watch for is preventing medium porosity from shifting toward high porosity through cumulative damage. Minimising heat, being careful with chemical processing, and using protective styles are all relevant.
Why this matters more than product ingredients alone
The same product can work beautifully for one person and do nothing or feel heavy for another because of porosity differences. Knowing your porosity explains why. When you see a review saying “this is the best conditioner I’ve ever used” and your experience is that it made your hair greasy and flat, you’re likely looking at a high-versus-low porosity difference in the reviewers.
Once you know your porosity, product selection becomes much more logical. You stop wasting money on products designed for different hair structure, and you can adapt techniques to what your hair actually needs rather than what a generic recommendation suggests.