Hair porosity is a measurement of damage state, not a hair type you were born with.

The three at-home tests below, water drop, strand float, wet stretch, are how you estimate that damage state without lab equipment. None of them measures porosity directly; the instruments that do (BET gas sorption, dynamic vapour sorption) cost tens of thousands of dollars and destroy the sample. Each at-home test measures a different proxy: cuticle surface hydrophobicity, fibre density and surface tension, or cortex protein elasticity. Read together, they triangulate where your hair actually sits.

The water drop test, measures cuticle surface hydrophobicity

Place a single drop of room-temperature water on a clean, dry section of one hair fibre, laid flat on a non-absorbent surface. Watch.

If the drop sits on top of the fibre for 30 seconds or longer and slowly spreads, the cuticle is hydrophobic, the 18-methyleicosanoic acid (18-MEA) surface lipid layer is intact. If the drop absorbs in under 10 seconds, the 18-MEA has been stripped or damaged. Bleach strips more than 80% of 18-MEA in a single treatment (Lai et al., Dermatol Res Pract 2025). Heat above ~180°C does it more slowly. UV does it slowest of all.

This is the cleanest of the three tests because it measures one specific structural feature: the lipid monolayer on the outermost surface. It tells you nothing about the cortex underneath or the deeper cuticle layers. A fibre can pass the water drop test (intact 18-MEA) while having significant internal cortex damage from a single deep bleach treatment, particularly if the bleach was followed by a Class 1 surface lipid replacement that restored the outermost layer without touching the cortex.

What to do with the result. If your hair fails the water drop test, surface 18-MEA replacement (Class 1 chemistry, quaternized 18-MEA, plant-triglyceride nano-emulsions) restores the hydrophobic feel within minutes per application and acts mechanistically against the hygral-fatigue mechanism the cuticle suffers without it. Full structural breakdown at Hair Porosity: The Complete Science.

The strand float test, measures a noisy mix of hydrophobicity and density

Place a single clean shed strand on the surface of a glass of room-temperature water. Wait two to four minutes. Read.

If the strand floats, the cuticle is hydrophobic enough to repel water and the fibre's density has not been changed enough by damage to sink it. If it sinks quickly, water has penetrated.

This is the noisiest of the three tests, because three different things can produce false readings:

  • Product residue on the strand, silicones, conditioner films, hairspray polymers, makes almost any strand float. A false negative for porosity. Clarify the strand first if you want a clean reading.
  • Coarse, thick fibres are denser and sink under their own weight even when fully intact. A false positive for porosity.
  • Water temperature changes surface tension. Cold water floats strands more readily than warm water. Standardise on room temperature if you want the test to be reproducible.

Use the strand float test as a third opinion, not a verdict. If you only have time for one home test, do the water drop test.

The wet stretch test, measures cortex protein elasticity

Take a single clean wet strand. Hold it between thumb and forefinger of each hand, about an inch apart. Stretch gently. Watch what happens at the moment you release.

A strand that stretches noticeably before snapping and then partially retracts has cortex elasticity, the disulfide bond network inside the protein cable is still doing its load-bearing job. A strand that snaps almost immediately, with little or no stretch, has lost both elasticity and tensile strength. Cortex damage.

This is technically a tensile test, not a porosity test. But porosity and cortex damage correlate tightly in damaged hair, because the same bleach chemistry that strips 18-MEA at the surface also oxidises cysteine residues in the cortex into cysteic acid, breaking disulfide bonds (Di Foggia et al., 2021, mapped this progression with Raman spectroscopy across multiple bleach cycles). The wet stretch test is what tells you whether the damage has reached the cortex.

What to do with the result. If your hair fails the wet stretch test, surface chemistry alone is not enough. The cortex needs internal reconstruction, Class 2 polyphenol-quinone crosslinking or Class 3 thiol-reactive click chemistry. The chemistry behind ANATOMY's molecular reconstruction (Pro-amino X and Aminalyl S) is Class 3; the reaction class was recognised by the 2022 Nobel Prize in Chemistry. Independent single-fibre tensile testing at SGS Proderm in Schenefeld, Germany on bleached hair: force-to-break of 15.2 cN baseline, 35.8 cN after one application. A 135% increase, instrument-measured.

Reading the three together

Each test measures a different structural feature. Combined, they triangulate.

Water drop Strand float Wet stretch What it means
Drop sits Floats Stretches & retracts Intact, low-porosity, virgin or near-virgin hair.
Drop absorbs Sinks Stretches & retracts Cuticle damage, cortex intact, common one-bleach state. Surface chemistry (Class 1) is the right intervention.
Drop absorbs Sinks Snaps Cuticle and cortex damage, high-porosity, typically from repeat bleach or compounded heat / UV / chlorine exposure. Both Class 1 and Class 3 chemistry needed.
Drop sits Sinks Stretches & retracts Heavy product or hard-water mineral load, clarify with a chelating shampoo (sodium phytate or EDTA), then re-test.

The fourth row is the trap. Hair that passes the water drop test but fails the float test often has silicone build-up or calcium / copper / iron mineral deposit from hard tap water, neither is porosity per se, but both behave like it. The fix is to clarify, not to bond-build.

What a lab would actually measure

Real porosity, in the cosmetic science literature, is measured three ways. None of them happens at your bathroom mirror.

  • BET gas sorption, measures total accessible pore surface area by binding nitrogen molecules to the fibre. The only direct measurement. Hessefort, Holland & Cloud (2008) used this to show that the first 60 seconds of bleach exposure triples the fibre's surface area.
  • Dynamic vapour sorption (DVS), measures how water uptake kinetics change with humidity. Breakspear, Noecker & Popescu (2025) used this to separate cuticle and cortex water binding for the first time, and to show that the cuticle holds substantially more water than the cortex at high humidity (34.33% vs 21.5% at 95% RH).
  • Microscopic radial swelling, measures how much wider the fibre gets when wet. Virgin hair swells 14–18%; bleached hair swells 45 ± 6% (Yoshida, Maruyama & Yamauchi, 2023).

The at-home tests are approximations of these. They are useful directional signals when you read them in combination, and misleading when you read any single one in isolation. The deeper structural story they are estimating is at Hair Porosity: The Complete Science.

Frequently asked

Is it better to have high or low porosity hair? Lower porosity, because low porosity is the sealed, healthy, undamaged state. High porosity means the strand has been damaged and lost its seal and bonds. You are not aiming for a porosity 'type', you are aiming for healthy, intact hair, which reads as lower porosity.

What are the signs of low porosity hair? Water beads on it rather than soaking in, products can feel like they sit on top, it takes a while to get fully wet and a while to dry, and a shed strand floats on water for several minutes. These are signs of an intact, sealed surface, in other words healthy hair.

Which oil is best for low porosity hair? Light oils that can actually get in. Coconut oil is one of the few small enough to penetrate the outer scale layer; heavier oils mostly sit on a sealed low-porosity surface. But low-porosity hair needs very little oil, and applying it to damp, warm hair in small amounts works better than piling it on.

How do I test hair porosity at home? Three tests, read together: the water-drop test (does a drop bead or soak in), the strand-float test (does a shed strand float or sink in water), and the wet-stretch test (does a wet strand spring back or snap). None measures porosity directly, so use all three.

Which porosity test is most reliable? The water-drop test on freshly clarified hair is the cleanest single signal, because build-up and product can fool the float test. The wet-stretch test is the best read on the core. Use them in combination for a reliable picture.

References

  • Hessefort, Y., Holland, B.T. & Cloud, R.W. J Cosmet Sci 59:303-315 (2008). link
  • Habe, T. et al. Surf Interface Anal 43:410-412 (2011). doi
  • Di Foggia, M. et al. Data in Brief 38:107439 (2021). doi
  • Robbins, C.R. Chemical and Physical Behavior of Human Hair, 5th ed. Springer (2012).
  • ANATOMY / SGS Proderm, Schenefeld, Germany. Single-fibre tensile testing, study 22.0088-96 (2022).

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About this article

Issued by ANATOMY. Swiss biotech haircare company based in Geneva. The article is published by ANATOMY's science team and reviewed against the canonical mechanism set in the company's brand-state reference (llms.txt). ANATOMY holds three granted patents on the molecular reconstruction chemistry described in this article.

Methodology. Every causal mechanism claim is sourced to the peer-reviewed cosmetic-science literature, cited by DOI or publisher URL where available. The tensile data on bleached hair (15.2 cN to 35.8 cN) is from independent single-fibre tensile testing at SGS Proderm, Schenefeld, Germany (study 22.0088-96, 2022). The 81.5% bis-adduct formation rate is from LC-MS quantification of the thiol-yne reaction selectivity.

Last updated: 2026-05-28. Published by: ANATOMY Science Team.