Hair Porosity: Facts, Assumptions, and What a Buyer Can Actually Observe
A strand floats in a glass of water and is described as low-porosity hair. Another feels rough between the fingers and is described as highly porous. A glossy bundle is presented as healthy and unprocessed.
Demonstrations like these circulate widely on social media. Each records something real about a sample at a particular moment. What I find worth examining is the distance between what each demonstration records and the conclusion attached to it.
Porosity is a genuine subject of scientific investigation. The difficulty arises when several distinct properties of a hair fibre are compressed into a single label, and that label is then treated as a statement of quality.
What researchers mean by porosity
In materials science, porosity refers to the void space within a material. Hair researchers have quantified it as total pore volume, pore-size distribution and internal surface area. Hessefort and colleagues used gas sorption to make these measurements on bleached and UV-exposed hair [1]. Habe and colleagues later applied thermoporometry, which infers pore size from the thermal behaviour of water confined in pores, and reported results in good agreement with other methods of measuring hair porosity [2].
The float test records how one strand meets water under one set of conditions. It does not measure pore volume.
Several other properties are often discussed under the same word, but each is measured differently:
Surface wettability: how readily water spreads over the outside of the fibre.
Water sorption: how much moisture the fibre takes up under defined conditions.
Sorption kinetics: how quickly that uptake occurs.
Swelling: how the fibre’s dimensions change as it absorbs water.
Mechanical performance: how the fibre behaves under tension or other forces.
These properties can be related, but none substitutes for another. Research using dynamic vapour sorption has modelled moisture uptake in the cuticle and the cortex separately [3]. Earlier work from the same group found that the cuticle’s role in moisture management becomes more significant at higher relative humidity [4]. Neither finding reduces to an image of cuticle scales simply opening and closing.
The labels “low”, “medium” and “high” may be convenient shorthand. Without a stated method, reference sample and test conditions, however, they do not tell a buyer what was actually measured.
What changes a fibre’s properties
The surface. The outer surface of the cuticle carries a covalently bound fatty acid, 18-methyleicosanoic acid (18-MEA), which makes the surface hydrophobic and reduces friction. Alkaline treatments such as colouring and perming can remove it, after which the surface becomes more hydrophilic and friction increases [5]. The relationship is not one-to-one. A 2019 review reports that bleaching alone did not cause complete loss of hydrophobicity even after 18-MEA was removed; additional weathering, such as repeated shampooing, was required [6].
The interior. Bleaching also changes internal pore structure, and not in a single direction. Working with commercially supplied hair described as virgin, Hessefort et al. found that bleaching nearly tripled its internal surface area within the first minute, followed by a sudden drop after ten minutes, which they interpreted as smaller pores breaking down into larger ones [1]. Habe et al. similarly concluded that bleaching adds smaller pores, while prolonged bleaching appears to produce fewer but larger cavities, most likely through pore merging [2]. Hessefort et al. also observed that hair toward the root showed much less porosity than the tip ends [1]: a single strand is not uniform along its length.
Wear and grooming. A 2025 study took commercially supplied textured hair described as virgin, bleached part of it in the laboratory, and subjected both to repeated cycles of washing, blow-drying, combing and heat straightening. Both chemical and physical processes produced significant changes in water permeability, surface topography and appearance, together with reductions in mechanical and thermal properties [7]. The reductions were less pronounced in the bleached hair, which the authors suggest may reflect reduced heat conductivity from its increased porosity [7]. A result like this cautions against assuming that more treatment history always produces a proportionally worse outcome on every measure.
What touch and sight can suggest
A buyer or wigmaker may notice roughness, tangling, uneven lustre, differences between mid-lengths and ends, or changes in handling after washing. Framed as observations, these are useful: this sample feels rougher; these ends tangle more; this ponytail behaves differently after washing.
The difficulty begins when an observation is converted into a specific explanation without supporting evidence.
Smoothness is a clear example. In one study, an 18-MEA-based conditioner applied to colour-treated, weathered hair produced a hydrophobic surface that persisted after shampooing, and friction that was not significantly different from that of the study’s reference hair, which the authors describe as “normal hair” [8]. Related work from the same research group reports similar surface results [5, 6]. A smooth hand is therefore not, by itself, evidence of an undamaged interior or an unprocessed history.
Moisture behaviour is similarly more complex than “damaged hair absorbs water quickly and loses it immediately”. Dynamic vapour sorption shows that hair’s moisture content at a given humidity depends on whether that humidity is approached from the dry side or the wet side, a phenomenon known as sorption hysteresis [9]. The same study found that ordinary rinse-off conditioner actives showed limited moisturising capability [9].
Professional observation remains valuable. But it becomes more credible when its limits are stated.
The glass-of-water test
The float test asks a strand to do something very different from laboratory porosity measurement. Whether a fibre stays at the water’s surface depends on surface tension and on how readily the fibre surface wets. As the studies above show, surface wettability can be altered by conditioning treatments and by the state of the 18-MEA layer [6, 8]. Those are surface changes; they say nothing direct about internal pore structure. Residual oils and styling products may also influence the result.
I have not found a peer-reviewed study that validates the float test against an instrumental porosity method. That does not show the test always fails; it means its reliability has not, to my knowledge, been demonstrated. A floating strand is an observation of that strand under those conditions. It is not a measurement of pore volume, a validated three-level classification, or evidence of an unprocessed history.
Other common demonstrations
Demonstration | What it may show | What it does not establish on its own |
Running fingers along a strand | Direction-dependent friction; perceived roughness | Internal pore volume or complete treatment history |
Spraying water over a bundle | Surface wetting under those conditions | A quantitative porosity classification |
Comparing drying times | Drying behaviour of those samples in that arrangement | A measurement of internal porosity |
Showing shine or “silkiness” | Appearance and surface feel at that moment | Absence of coatings, internal damage or previous processing |
Demonstrating bleach uptake | Response to that particular chemical procedure | A unique explanation of the sample’s history |
These demonstrations are practical observations, but most informative when described as such.
What laboratory methods can reveal
Different methods answer different questions:
Gas sorption: accessible surface area, pore volume and pore-size distribution under a defined protocol [1].
Thermoporometry: pore size and size distribution, from the thermal behaviour of water confined in the fibre [2].
Dynamic vapour sorption: moisture uptake, release, hysteresis and kinetics as humidity is controlled [3, 9].
Microscopy (SEM, AFM, fluorescence): surface topography and structural deterioration, best read alongside swelling and mechanical data [7].
Contact-angle and friction measurement: surface wetting and lubrication, which help separate surface behaviour from assumptions about the interior [6, 8].
Tensile testing: mechanical performance after treatment; informative, but not a direct measurement of pore volume [7].
Each result describes the material tested, under the stated conditions.
How the research defines “virgin” hair
While checking the sources for this article, I looked at how each study describes the hair it uses as its untreated baseline. In the methods sections I was able to read, the baseline hair was either purchased from a commercial supplier and described as “virgin”, or donated by volunteers who reported that their hair had never been chemically treated. In none of those texts did the authors define the term or describe an independent check of the hair’s history. For several papers I could read only the abstract, and I cannot say how their baseline was established.
Study | Baseline hair, as described | Basis for that status |
Hessefort et al., 2008 [1] | “Virgin brown hair” | Purchased from a commercial supplier; term not defined |
Habe et al., 2025 [2] | “Virgin” hair fibres (abstract) | Full text not accessed |
Breakspear et al., 2024 [3] | “Untreated (virgin)” hair (abstract) | Full text not accessed |
Breakspear et al., 2022 [4] | “Virgin” fibres (abstract) | Full text not accessed |
Tokunaga et al., 2011 [5] | Not stated in the English abstract | Full text not accessed |
Tokunaga et al., 2019 [6] | Hair from volunteers with “no experience of chemical hair treatments” | Donor self-report; no verification described |
Gasparin et al., 2025 [7] | “Virgin textured hair”, washed with a surfactant solution before testing | Purchased from a commercial supplier; term not defined |
Tanamachi et al., 2009 [8] | “Normal hair” | Full text not accessed |
Kamath, 2020 [9] | European dark brown hair | Purchased from a commercial supplier |
This does not make the findings worthless. Most of the results cited here are comparisons: the same supplied hair measured before and after a controlled laboratory treatment. Those comparisons describe the effect of that treatment on that hair. What they cannot establish is the absolute condition of “virgin” hair, because the full history of the starting material is not documented. Throughout this article, results are therefore described relative to the hair as supplied.
Checks of this kind are not out of reach. Proof-of-concept work in forensic hair testing has identified candidate chemical markers of oxidative (bleaching) treatment [10]. In the methods sections I was able to read, no such check was reported.
I find it notable that a word carrying so much weight in the hair trade appears in parts of the research literature as a supplier’s or donor’s description rather than a defined and verified category. Several of these studies were also carried out by researchers affiliated with cosmetic product or ingredient manufacturers, as the papers state, and most used laboratory-prepared tresses under controlled conditions that may differ from commercial bundles. None of this invalidates the measurements. It does define what they can be used to claim.
What this means when buying hair
In procurement, I find it useful to keep three questions separate:
What can be observed? Appearance, feel, tangling and behaviour during an agreed sample assessment.
What has been disclosed? Processing, surface treatments and relevant handling history.
What has been measured? The method, sample selection, conditions and result behind any scientific claim.
Laboratory findings describe the samples tested. They should not be stretched into a complete account of a ponytail’s history or a guarantee about every strand in a shipment, particularly since porosity has been shown to differ between root and tip of the same hair [1].
Porosity is one aspect of a fibre’s structure and behaviour, not a new vocabulary for “good hair” and “bad hair”.
Beth Thompson - Founder, Lux Symbolica SASU, Paris. IATSE Local 706, Makeup Artists and Hair Stylists Guild. © 2026 Lux Symbolica SASU
References
[1] Hessefort YZ, 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. https://pubmed.ncbi.nlm.nih.gov/18818850/
[2] Habe T, Inoue S, Breakspear S, Noecker B, Popescu C. Thermoporometry measurements of human hair via differential scanning calorimetry. International Journal of Cosmetic Science. 2025;47(2):234–239. doi:10.1111/ics.13025 https://pubmed.ncbi.nlm.nih.gov/39284775/
[3] Breakspear S, Evans T, Frueh P, Neu A, Noecker B, Popescu C, Uellner Q. The kinetics of moisture sorption by hair. International Journal of Cosmetic Science. Published online 13 November 2024. doi:10.1111/ics.13028 https://doi.org/10.1111/ics.13028
[4] Breakspear S, Ivanov DA, Noecker B, Popescu C, Rosenthal M. Cuticle – designed by nature for the sake of the hair. International Journal of Cosmetic Science. 2022;44(3):343–362. doi:10.1111/ics.12782 https://doi.org/10.1111/ics.12782
[5] Tokunaga S, Tanamachi H, Inoue S, Morioka T, et al. Deposition of 18-MEA onto damaged hair to form a persistent hydrophobicity. Journal of Society of Cosmetic Chemists of Japan. 2011;45(3):190–198. doi:10.5107/sccj.45.190 https://doi.org/10.5107/sccj.45.190
[6] Tokunaga S, Tanamachi H, Ishikawa K. Degradation of hair surface: importance of 18-MEA and epicuticle. Cosmetics. 2019;6(2):31. doi:10.3390/cosmetics6020031 https://doi.org/10.3390/cosmetics6020031
[7] Gasparin RM, Lourenço CB, Leonardi GR. Porosity and resistance of textured hair: assessing chemical and physical damage under consumer-relevant conditions. Cosmetics. 2025;12(3):93. doi:10.3390/cosmetics12030093 https://doi.org/10.3390/cosmetics12030093
[8] Tanamachi H, Inoue S, Tanji N, Tsujimura H, Oguri M, Ishita M, Tokunaga S, Sazanami F. Deposition of 18-MEA onto alkaline-color-treated weathered hair to form a persistent hydrophobicity. Journal of Cosmetic Science. 2009;60(1):31–44. https://library.scconline.org/is-cacheable/1708709003777/18-MEA-Deposition-Color-Treated-Hair.pdf
[9] Kamath YK. Quantification of human hair moisturization with cosmetic products by dynamic vapor sorption. Journal of Cosmetic Science. 2020;71(5):303–320. https://library.scconline.org/v071n05/72
[10] Eisenbeiss L, Binz TM, Baumgartner MR, Kraemer T, Steuer AE. Cheating on forensic hair testing? Detection of potential biomarkers for cosmetically altered hair samples using untargeted hair metabolomics. Analyst. 2020;145(20):6586. doi:10.1039/d0an01265c https://doi.org/10.1039/d0an01265c
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