Hair Porosity Test: How to Check Low and High Porosity
Hair porosity is how readily your hair takes up water and how quickly it lets it go again, and a hair porosity test is a simple way to get a rough idea of yours at home. The usual checks are the float test, in which you drop a few strands into a glass of water to see whether they float or sink, and the strand test, in which you slide your fingers along a strand. Two other common checks are the spray test, in which you mist a section of hair with water, and noticing how fast your hair dries. We found no peer-reviewed study validating the float, strand or spray test, so treat the result as a hint and compare it with how your hair behaves on wash day.
What is hair porosity?
The cuticle is the outer layer of each hair, made of thin, flat cells that overlap like roof tiles over the cortex, the main body of the hair. Hair fibres are porous by nature, and a 2025 calorimetry study describes that porous structure as affected by physical and chemical influences from the environment and by cosmetic treatments such as bleaching. Researchers measure porosity with laboratory instruments, from gas sorption to calorimetry and dye uptake, not with a glass of water.
In a 2008 study, oxidative bleach nearly tripled the surface area of hair within the first minute because the number of pores went up. On bleached hair samples, a 2024 study found that UV light raised porosity from three hours of exposure onwards, and that particles from air pollution substantially increased it together with UV, though not on its own. A 2022 study describes surfactants, the cleansing agents in shampoo, as dissolving some of the hair's protein and raising its porosity once they get into the hair, and a 2015 review adds that rough washing, unprotected drying, friction, sunlight and alkaline treatments reduce the natural fatty layer on the hair surface, so the surface attracts water more readily.
The review also describes weathering as a gradual breakdown from root to tip through everyday grooming, so the ends of long hair have usually had the most wear. A pilot study found a moisture gradient from base to tip, and in the same study weathered hairs lost their moisture faster than intact ones. Our guide to frizzy hair explains how a worn cuticle and water in the air play into frizz.
How to do a hair porosity test at home
To test your hair porosity at home, drop a few clean strands into a glass of water, slide your fingers along a strand, mist a section with water and notice how quickly your hair dries, then read the results together. The float test is a common at-home method, but guides disagree on how long to wait, how many strands to use and how to read it: some call a floating strand low porosity, others a strand that floats for a while before sinking. There is no single correct procedure, so the table gives the usual reading.
| Test | What you do | Usual reading for low porosity | Usual reading for high porosity | Limit |
|---|---|---|---|---|
| Float test | Drop a few clean, product-free strands into a glass of water and watch for a few minutes. | Stays near the top, or floats for a while before sinking. | Sinks quickly. | Readings vary between guides; the surface and any product on it may affect the result. |
| Strand test (slide test) | Slide a finger and thumb along a strand from the tip towards the root. | Feels smooth. | Feels rough or bumpy. | Depends on touch and on any product in the hair; roughness can also mean the lengths are dry. |
| Spray test | Mist a small section of clean, dry hair with water. | Water sits in beads. | Water soaks in quickly. | Beading may say more about the hair's outermost layer than about its pores. |
| Wetting and drying time | Notice how long hair takes to get wet in the shower and to air-dry. | Slow to wet, slow to dry. | Wets and dries quickly. | Also depends on length, thickness and how warm and dry the room is. |
We found no peer-reviewed study validating the float test, the strand test or the spray test against a laboratory measurement of porosity. In a 1969 lab study, whether hair floats or sinks was used to measure its critical surface tension, a measure of how easily its surface wets, not its porosity, which suggests a floating strand may reflect its surface as much as its pores. Similarly, a 2011 study reads the time water droplets take to soak into hair as a sign of how intact its outermost fatty layer is.
Low porosity hair
Low porosity hair is the label hair care guides use for hair that is slow to take up water: it takes a while to get properly wet, sprayed water beads on the surface, it is slow to air-dry, and conditioner seems to sit on top. It is not a measured category.
How to care for low porosity hair
These tips come from hair care guides, not from studies of caring for hair by porosity type. Most guides suggest lighter products, a clarifying wash now and then to clear build-up, and conditioner on damp hair. A common tip is to go easy on protein treatments, since several guides report that low porosity hair can feel stiff with too much protein. If your hair already feels stiff and snaps easily, our guide to protein overload explains why too much protein and dryness are hard to tell apart, and what to check first. For light oils, our guide to hair oil overnight covers what studies have found.
High porosity hair
High porosity hair is the label for hair that takes up water quickly and lets it go quickly: guides describe it as getting wet almost at once, drying fast, and tending to frizz and tangle. The closest lab findings concern bleached and weathered hair, not a porosity type. In a 2022 infrared microscopy study, the researchers used labelled water that the instrument could track, and this water evaporated about an hour more slowly from untreated hair than from bleached hair. According to the 2015 review, bleached and chemically treated hair also attracts conditioning ingredients more readily, because it is more porous and carries more negative charge.
How to care for high porosity hair
Here too, the tips come from hair care guides rather than from studies of caring for hair by porosity type. Most guides suggest conditioner after every wash, a leave-in conditioner, gentle detangling and lukewarm rather than hot water, and a common tip is to space out bleaching and chemical treatments and trim worn ends regularly. The routine in our guide to dry hair applies here too, and our guide to damaged curly hair covers curls that have been bleached or chemically treated.
Can you change your hair porosity?
You cannot undo porosity that comes from worn or chemically damaged hair, but you can limit new wear, and hair growing in from the root has had the least weathering. Conditioners change how hair feels while they are on it. Structural damage is a different matter and cannot be repaired: a damaged cuticle does not close back up, and most care products work mainly on the surface. Care cannot rebuild a cuticle that has been worn away. A cold final rinse is a popular tip, but there is little evidence that it closes the cuticle or adds shine. Our guide to shiny hair covers what does change how hair looks.
Based on the studies above, limiting new wear means fewer rounds of bleaching and chemical treatments, less unprotected sun, and gentler washing, drying and handling. As you trim, new growth gradually replaces the most worn lengths.
Everyday friction, night included
Everyday rubbing is part of the wear that builds up in hair. The 2015 review names abrasion and friction among the factors that damage hair through protein loss, and at night your hair moves against the pillowcase each time you turn over. On friction, silk usually has the edge: its smooth, dense surface creates less friction against hair than a cotton weave does. A pillowcase does not repair hair that is already damaged. Our comparison of cotton vs silk pillowcases covers the other differences between the two fabrics.
What a porosity test cannot tell you
A home test looks at a few strands, or at your hair on a single wash day. Porosity varies along a hair, since the ends have usually weathered more than the roots, and between people in ways that do not fit a simple scale. A 2020 study found that African hair was more permeable, Caucasian hair took up more water as humidity rose but let it spread through slowly, and Asian hair was more resistant to changes in hydration. A porosity result therefore does not diagnose damage or choose products for you: it is one clue to read alongside how your hair looks, feels and behaves.
What our silk pillowcases are made of
The RENESSY silk pillowcases use 100% organic mulberry silk with a weight of 22 momme, and both faces of each case are silk. Mulberry silk comes from silkworms raised on the leaves of the mulberry tree, and momme measures the weight of silk fabric. The raw silk is rated grade 6A, the top class in the Chinese raw-silk standard (GB/T 1797). GOTS, the Global Organic Textile Standard, certifies textiles made from organically grown fibres. The silk is GOTS certified. OEKO-TEX MADE IN GREEN is a label for textiles tested for harmful substances and made in traceable, certified production. The pillowcases carry the OEKO-TEX MADE IN GREEN label, and the label ID M27MNB1V9 can be checked on the OEKO-TEX website. The pillowcases carry the Dermatest 5-Star seal and the Dermatest Sensitive Skin seal, dermatologically tested for sensitive skin. A hidden YKK zip closes each case.
Frequently asked questions
Is the hair porosity float test accurate?
The hair porosity float test is a common at-home method, but we found no peer-reviewed study validating it, and guides disagree on how to read it. Use clean hair and several strands, and treat the result as a rough hint.
Is hair that dries quickly low or high porosity?
Hair care guides usually read hair that dries quickly as high porosity, and lab studies found that bleached hair loses water faster than untreated hair and that weathered hair loses it faster than intact hair. Length, thickness and how warm and dry the room is also affect drying time.
Is curly hair always high porosity?
No study we found shows that curly hair is always high porosity: the 2020 study found African hair more permeable, but it compared groups of people, not curl patterns, and did not sort hair into porosity types. The lab evidence for higher porosity is clearest for bleaching and other chemical treatments, for UV on bleached hair, and for everyday wear.
Can hair have different porosity at the roots and the ends?
Yes, hair can have different porosity at the roots and the ends, because weathering builds up from root to tip, so the ends have had the most washing, brushing, sun and treatment.
Sources
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- Fuse N, Matsui M, Matsue Y. Temporal and spatial visualization of water uptake into human hair studied by infrared microscopy. Analytical Sciences. 2022;38(3):601-605. doi:10.1007/s44211-022-00074-x
- Gavazzoni Dias MF. Hair cosmetics: an overview. International Journal of Trichology. 2015;7(1):2-15. doi:10.4103/0974-7753.153450
- Habe T, Inoue S, Breakspear S, et al. Thermoporometry measurements of human hair via differential scanning calorimetry. International Journal of Cosmetic Science. 2025;47(2):234-239. doi:10.1111/ics.13025
- Hessefort Y, Holland BT, Cloud RW. True porosity measurement of hair: a new way to study hair damage mechanisms. Journal of Cosmetic Science. 2008;59(4):303-315. PMID 18818850
- Kaushik V, Kumar A, Gosvami NN, et al. Benefit of coconut-based hair oil via hair porosity quantification. International Journal of Cosmetic Science. 2022;44(3):289-298. doi:10.1111/ics.12774
- Oliver MA, Coderch L, Carrer V, et al. Ethnic hair: thermoanalytical and spectroscopic differences. Skin Research and Technology. 2020;26(5):617-626. doi:10.1111/srt.12842
- Piérard-Franchimont C, Piérard GE. Hair weathering and hair capacitance mapping: a pilot study. Journal of Cosmetic Dermatology. 2012;11(3):179-182. doi:10.1111/j.1473-2165.2012.00620.x
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- Yang SJ, Yu HJ, Lee J, et al. Effects of ultraviolet rays and particulate matter on hair porosity in damaged hair. Journal of Cosmetic Dermatology. 2024;23(11):3735-3739. doi:10.1111/jocd.16442