Hair Types & Porosity · Guide
Porosity is how readily your hair takes in and holds water, and it governs whether product sinks in or sits on top. Three practical tests take five minutes, and the popular float-a-strand-in-water version is the least reliable of them.
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Every hair strand is wrapped in a cuticle: overlapping scales, like roof tiles. Porosity describes how tightly those scales sit, and therefore how easily water and product get in and out.
This is not a folk concept. Porosity is a measurable physical property of the fiber, and researchers assess it directly as a way of studying hair damage (true porosity measurement of hair, PubMed). It also changes with chemical processing: bleaching, for instance, substantially increases it (straightening and bleaching microstructure study, PMC).
Practically, it is the second most useful thing to know about your hair after strand thickness — and unlike curl type, it changes what you should actually buy.
1. The water-absorption test. Start with clean, dry, product-free hair. Run a section under water. Does it soak in immediately and go heavy, or does water bead and roll off while the hair stays stubbornly dry underneath?
2. The drying-time test. After washing, roughly how long does your hair take to air dry? Low porosity hair takes a long time — the cuticle that would not let water in will not let it out either. High porosity hair dries fast.
3. The slide test. Take one shed strand, hold it at the tip, and slide your fingers up towards the root. Smooth means low porosity. A bumpy, catchy texture means the cuticle is raised — high porosity.
Two out of three agreeing is enough. If they disagree, trust the drying-time test — it is the hardest to get wrong.
The famous version: drop a shed hair into a glass of water and see whether it sinks (high porosity) or floats (low porosity).
The problem is surface tension. A single hair is light enough that surface tension holds it up almost regardless of porosity, and any residue on the strand — conditioner, silicone, oil — makes it more hydrophobic and more likely to float. People with high porosity hair routinely get a "low porosity" result from it.
It is not useless, but treat it as the least reliable of the four and never as the decider.
Low porosity. The cuticle is tightly packed and resists letting things in. Product sits on the surface and feels greasy; hair takes forever to wet and forever to dry; heavy oils and butters do nothing useful. You want lightweight products, gentle warmth to help them in, and clarifying more often than you would expect because buildup has nowhere to go. See products for low porosity hair.
Medium porosity. The comfortable middle. Most products work as intended, hair holds a style, and there is no particular constraint to design around.
High porosity. The cuticle is raised or damaged. Hair drinks water and product and still feels dry an hour later; it frizzes the moment the air is humid; it takes color fast and loses it fast. You want heavier products, protein, and a sealing step. See products for high porosity hair.
You are born with a cuticle structure, but bleaching, permanent color, relaxers, heat and even years of mechanical wear all raise porosity. Almost nobody gets less porous over time without cutting the affected length off.
Which means two things. Your ends are usually more porous than your roots, because they are older and have been through more — so it is entirely normal to treat them differently. And if your hair used to behave one way and now behaves another, porosity change is a likely explanation.
From the picks
A lightweight leave-in if you came out low porosity, a rich mask if you came out high, and a sealing oil for high-porosity ends. Buy the one that matches your test, not all three.
Best for fine curls
The curl cream for people whose curls collapse under a normal curl cream. Curlsmith builds it on hyaluronic acid rather than heavy butters, so it hydrates without the weight.
Best weekly mask
The straightforward weekly deep conditioner, built on oils and B-vitamins rather than a patented bond active. When hair is thirsty rather than structurally broken, this is the honest answer.
Best finishing oil
The product that started the argan-oil category and still the most useful version of it: a few drops through damp lengths smooths the cuticle and cuts drying time.
Once you know your porosity, the other half of the picture is strand thickness — and the two together are what the routine guide is built around.
We have not used these products ourselves. They are chosen from what is in the formula, what those ingredients are documented to do, and whether that matches the problem this page is about — and every product below links to the manufacturer's own page so you can check the formulation claims yourself. The full method is here.
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Claims about what an ingredient does are cited to dermatology bodies or published research. Claims about what a product contains are cited to the manufacturer's own page and labeled as the manufacturer's claim. Where the evidence is thin, we say so on the page rather than rounding it up. Read the full method.