How to Tell Your Hair Porosity at Home (and Why It Changes Everything)
Most hair advice quietly assumes that every head of hair behaves the same way. It doesn’t. Porosity — how readily your hair takes in moisture, and how well it holds on to it once it has — is probably the single most useful thing you can know about your own hair. It is also the reason a conditioner that transformed your friend’s curls left yours flat, greasy and somehow still dry underneath.
What porosity actually describes
Every strand of hair is wrapped in a cuticle: a layer of overlapping cells arranged rather like roof tiles. When those tiles lie flat and tight, water struggles to get in — but once it is in, it struggles to get out again. When they sit raised or damaged, water floods in quickly and evaporates just as fast.
That is the whole concept. Low porosity means a tight cuticle. High porosity means a raised or broken one. Neither is better; they simply need opposite things, which is why generic advice fails so many people.
The float test, and why you should ignore it
You have probably seen it: drop a shed hair into a glass of water, wait, and see whether it sinks. Sinking supposedly means high porosity.
In practice the test measures surface tension and product residue far more than it measures your cuticle. A strand with silicone on it will float regardless. A strand you touched with slightly oily fingers will float too. Trichologists have been pointing this out for years, and it remains the most repeated piece of misinformation in hair care. Skip it.
Two tests that actually tell you something
The drying-time test. Wash your hair with a clarifying shampoo and no conditioner, squeeze out the excess with a towel, and leave it to air dry with nothing on it. Note how long it takes to dry completely. Under about an hour suggests high porosity — water is leaving as easily as it arrived. Three hours or more, especially if the hair still feels damp at the roots, points to low porosity.
The water-bead test. On clean, product-free dry hair, drop a little water onto a section and watch. If it beads up and sits on the surface for several seconds before soaking in, your cuticle is tight: low porosity. If it vanishes almost instantly, it is raised: high porosity.
Run both. If they agree, you have your answer. If they disagree, you are probably somewhere in the middle, which is genuinely common.
If your hair is low porosity
Your problem is getting moisture in, not keeping it there. Heavy butters and thick creams will sit on the surface and build up, which reads as greasy roots and dull, coated lengths.
Work with warmth instead. Apply conditioner to damp — not soaking — hair, and leave it under a warm towel or shower cap for ten minutes; the gentle heat lifts the cuticle just enough. Choose lightweight, water-based products where water is the first ingredient. Clarify every few weeks to shed the residue that inevitably accumulates. Humectants such as glycerin and honey tend to serve you well.
If your hair is high porosity
Getting moisture in is easy. Keeping it in is the battle. High porosity is usually earned rather than inherited — bleach, heat, and years of friction raise the cuticle — though some people are simply born with it.
Seal aggressively. Layer a leave-in conditioner, then a cream, then an oil or butter on top to lock the water in. Use protein treatments periodically to patch the gaps in the cuticle, but not weekly: too much protein makes hair stiff and brittle. Rinse with cool water at the end of a wash to encourage the cuticle to lie flatter, and sleep on silk or satin to cut down the overnight friction that keeps reopening it.
If your hair is medium porosity
Medium porosity hair holds style well, takes colour predictably and tolerates most products. The main risk is complacency — heat and chemical processing will push you toward high porosity over time. A light protein treatment every six to eight weeks and a heat protectant whenever you use tools is genuinely enough.
Porosity is not fixed, and not uniform
This is the part most guides leave out. Your porosity changes. Bleach raises it permanently. Heat raises it gradually. Age and hormonal shifts alter it too.
It also varies along a single strand. If you have grown out colour, the roots may be low porosity while the ends — older, more processed, more weathered — are high. That is why the ends drink up oil while the roots turn greasy from the same product. Treating your hair as two different textures is not fussy; it is accurate.
Turning the result into a routine
Change one thing at a time and give it three to four weeks. Hair responds slowly, and stacking five new products at once tells you nothing about which one helped.
Start with the step that matches your result most directly: warmth during conditioning for low porosity, a sealing layer for high porosity. Judge it on how your hair feels the day after washing, not the hour after. That delayed verdict is where the truth usually lives.
