Zoltan Hair teCsture · Diagnostics · Up Library
The Hair Porosity Guide
Porosity is how fast your hair takes a chemical in, and the reading everyone gets backwards is the direction it points: damaged hair does not resist lotion, it drinks it.
Porosity has become a home-care word, tested in a glass of water and used to sell conditioner. In a salon it is a working measurement that sets lotion strength, sets timing, and sometimes ends the appointment. This is what it means and how it is actually read.
Also known asCuticle condition · absorption rate · 18-MEA loss
- What it measures
- 18-MEA loss The bound lipid layer that waterproofs healthy hair.
- Tiers
- Three Low, medium, high — and most heads carry two of them at once.
- Damage means
- Faster Porous hair takes lotion in several times quicker, not slower.
- Float test
- Unreliable Residue and surface tension move it more than the hair does.
- Bleached hair
- Usually no Judged on the hair in front of me, not from a page. Assume no.
What porosity actually measures
The usual definition — how readily hair absorbs and retains moisture — is true and tells you almost nothing about why. The why sits in two places.
The first is the cuticle: overlapping protein scales, like roof tiles, wrapped round the cortex where the disulphide bonds live. When they lie flat and tight, very little gets past them. When they are lifted, gapped or missing, a great deal does.
The second is the part most descriptions leave out, and it is the one that makes porosity predict anything. Bound to the outside of the cuticle is a lipid layer whose principal component is 18-MEA, 18-methyleicosanoic acid, held on through thioester linkages. It is a wax coat, and it is why virgin hair beads water at the basin rather than soaking. Alkaline oxidative conditions cleave those linkages — which is to say bleach, permanent colour, chemical straightening, previous perms and sustained heat all take it off. Once it is gone it does not come back. Conditioners imitate the feel of it. Nothing replaces it.
Porosity is not a measure of dryness. It is a measure of how much 18-MEA the hair has lost, and therefore how fast anything you put on it will reach the cortex.
That is why two clients with identical-looking hair respond differently to the same lotion, and why a stylist who reads porosity by hand can tell you what will happen before anything is mixed.
Damage does not make hair harder to process
The instinct is that damaged hair is tough, dry and stubborn, so it must need more. It needs less, and it needs it for less time.
Damage does not make hair harder to process. It makes it dangerously easy.
Hair with no lipid layer and a raised cuticle takes liquid in several times faster than the hair growing out of your scalp today. So the ends — three years old, coloured, heat-styled, weathered — over-process while the roots are still working. That single gap is what almost every protective technique in this library exists to manage: barrier creams, dual-lotion applications, porosity equalisers, protective pre-wraps, staggered timing. None of them is fussiness. They exist because one head is running at two speeds.
It also explains a sentence clients hear and disbelieve: your hair looks dry because it cannot hold moisture, not because it will not let chemicals in. Dryness and resistance are different properties. The same strand can be both parched and wide open.
And the label that trades on the confusion
“For damaged or porous hair” on a perm box means a milder reducing agent — a sulphite system, cysteamine, an acid-balanced formula. Those swell the cuticle less and they are worth having. They still require intact disulphide bonds to work with. A gentler chemical on hair that has lost its bonds is a gentler way of achieving nothing.
The three tiers, and what each one means at the rod
Low
Sealed
Scales lie flat and overlap tightly, lipid layer intact. Water beads rather than soaking in; slow to saturate in the shower, slow to air-dry. Shiny, resilient, and resistant to chemical penetration.
At the rod: difficult to perm, not impossible. A standard lotion struggles to reach the cortex, so a stronger alkaline formulation is usually indicated, and the wave will drop within days if the strength is wrong.
Medium
Normal
Scales slightly raised, so moisture, treatments and lotion enter smoothly and stay in the cortex. Absorbs water easily, feels smooth, holds a style, needs little intervention to look well.
At the rod: the ideal canvas. Takes standard thio lotions predictably, processes evenly, rebuilds cleanly at neutralisation, and gives the best curl longevity for the least structural stress.
High
Open
Scales gapped, lifted, damaged or missing, lipid layer largely gone — from cumulative chemical work, heat, mechanical friction or sun. Absorbs water instantly, tangles, dries fast because it cannot hold anything.
At the rod: a red flag. Lotion enters fast and unevenly, over-processing the most damaged sections while the rest is still working, and the result is breakage rather than curl.
Where high porosity means the bonds have gone
Where it comes from bleach the answer is usually no, and usually is doing real work in that sentence: bleaching converts cystine to cysteic acid, the neutraliser needs two sulphur atoms, and there is nothing left to rebuild, so most of this hair takes a curl that drops out within weeks while the hair pays for it. That is the default and the default is no, and the exception is a judgement made on the hair in front of me rather than a gentler lotion. Highlights and foils count. Where it comes from a hydroxide relaxer, there is no perm either, for a separate reason — lanthionisation permanently removes one sulphur, and thio and hydroxide never meet on the same strand in either direction. Both are covered in full on bleach damage.
The mistake that is made on resistant hair
The obvious answer for a stubborn low-porosity head is a stronger alkaline lotion and a little heat under a hood dryer to open the cuticle. That combination is a real error, not a shortcut. An alkaline wave already carries substantial chemical swelling, and external heat then drives the reducing agent into the cortex far faster than any timer anticipates, with added risk to the scalp.
There are two valid routes and they are either-or: a stronger alkaline lotion at room temperature, or an acid wave, which is endothermic and needs heat by design. Never both at once.
The numbers that sit behind the reading
Porosity decides which of these a head can take, so they belong on the same page. Healthy hair and scalp sit acid, at around pH 4.5 to 5.5. Everything a perm does moves away from that and then comes back.
| Where | pH | What it does |
|---|---|---|
| Hair and scalp at rest | 4.5–5.5 | Cuticle closed and flat. The state everything returns to. |
| True acid perm | 6.9–7.2 | Minimal swelling. Needs heat, because it is endothermic. |
| Acid-balanced perm | 7.8–8.2 | The middle ground. Some swelling, more reliable curl. |
| Alkaline (cold) perm | about 9–9.5 | Swells the cuticle enough for the reducing agent to reach resistant hair. |
| Peroxide neutraliser | 2.5–4.0 | Oxidises the bonds closed and drops the pH back down. |
| Bromate neutraliser | 6.0–7.0 | Slower, gentler oxidation at close to neutral. |
The regulatory ceiling is worth knowing, because it settles arguments. In Great Britain and the EU, a ready-for-use perm lotion may not exceed pH 9.5, with thioglycolic acid limited to 8 per cent in general-use products and 11 per cent professional. Anything quoted above that ceiling is either not a perm lotion or not legal here. pH and perms takes both halves of that further.
Read against porosity, the table reads simply. Low porosity generally needs the top of it. High porosity cannot safely be given the top of it, which is the whole difficulty: the hair that needs the gentlest chemistry is often the hair that was going to need the strongest.
How porosity is actually read, and what to ignore
In the chair it takes about two minutes and it is done by hand. Fingers run up a damp strand from point to root, against the direction of the scales, feeling for friction. Smooth and slippery is a closed cuticle. Rough, catching, squeaking is a lifted one. It is done at the root and again at the ends, because on most heads those are two different answers.
Then, and separately, elasticity: a wet strand stretched slowly between the fingers of both hands. Elasticity is what this library calls bounce, and bounce is disulphide bond health. It is the more important of the two readings by some distance, and it is described in full on the diagnostic page.
Over any tinted head, and over any head where the two readings disagree, there is also a strand test with the real lotion at the real strength. That is not optional and it is not a formality.
The float test
The method everyone has read about — a clean shed strand dropped into room-temperature water, floating for low porosity, sinking for high — is a rough indication at best, and the caveat should come before the method rather than after it. Surface tension, and any trace of oil or product residue, affect the result more than the condition of the hair does.
A stylist reading friction and elasticity by hand will be considerably more accurate than a glass of water, and neither the glass nor the hand replaces a strand test.
On the record, since the training literature is inconsistent about it: the American cold-wave patents of 1938 and 1939 belong to Arnold F. Willat — one T, of San Rafael, California — and they use alkaline sulphides and sulphites rather than thioglycolate. The thioglycolate cold wave is Everett G. McDonough’s 1941 application. Porosity diagnostics were formalised into professional curricula later still, as chemical services multiplied. The cold wave covers the sequence properly.
Porosity and damage are two different questions
They are close enough that the words get used interchangeably, and the distinction changes what can be done, so it is worth being exact.
Porosity describes the cuticle and its lipid layer — the surface. It tells you how fast a chemical will go in.
Damage describes the cortex underneath — the bonds. It tells you whether there is anything for the chemical to work with.
Hair can be moderately porous from weathering, sun and years of blow-drying while its disulphide bonds remain largely intact. That hair has usable elasticity and can often be processed with care, on a milder chemistry and a shorter time. Hair that is porous because it was bleached has lost the bonds themselves, and no amount of conditioning, protein or porosity equaliser brings those back.
Porosity is a speed reading. Elasticity is the verdict. A stylist who takes only one of them is guessing at the other.
This is also why a client who has been told their hair is “high porosity” by an online quiz has not been told whether they can have a perm. Those are separate findings, and only one of them can be taken at a distance.
What porosity changes about home care
Porosity dictates aftercare more usefully than hair type does, because it describes what the surface will actually do with the product you put on it.
Low porosity. Lightweight moisture and gentle warmth. A heavy mask on a sealed cuticle sits on top of the hair and weighs it down without ever getting in; a little heat under a towel or a cap while conditioner is on does more than a richer product would.
High porosity. Protein and moisture balanced against one another, alternated rather than combined. Protein alone stiffens the fibre until it snaps; moisture alone leaves it soft and shapeless. Permed high-porosity hair loses its curl definition first at the ends, which is where the alternation is aimed.
The London problem, and it is a real one
Hard water leaves mineral deposits on and in the fibre. They act like microscopic grit: the hair goes rigid, feels crunchy, and reduces its own apparent bounce without any bonds having been lost. On permed hair this reads as a dropped curl, and on white or very fair hair the trapped iron and copper turn yellow the moment alkaline lotion or a peroxide neutraliser reaches them. A monthly chelating wash is not a refinement here, it is maintenance.
And one honest limit, since this page is about a surface. Nothing in home care rebuilds 18-MEA. Products that claim to replace it deposit something that behaves a little like it for a few washes, which is genuinely useful and is not the same thing. The bound layer you were born with is a one-way account.
Questions
What is hair porosity?
How readily your hair absorbs and holds moisture and chemicals, decided by the condition of the cuticle and, more particularly, by how much of the bound lipid layer on its surface is still there. That layer, principally 18-MEA, is what makes healthy hair water-repellent. Porosity is essentially a measure of how much of it has been lost.
How do I test my porosity at home?
Treat the float test as a rough indication at best. Surface tension and any oil or product residue affect the result more than the hair’s condition does. A more useful home reading is to run your fingers up a damp strand towards the root and feel for friction: smooth means a closed cuticle, rough and catching means a lifted one. Do it at the ends and near the root, because they will often disagree.
Can low-porosity hair be permed?
Yes, and it often perms very well. It needs a stronger alkaline formulation and accurate timing, because a lotion that is too mild will not reach the cortex and the wave drops within days. What it must not have is a strong alkaline lotion plus external heat — that combination over-processes and adds risk to the scalp. Stronger lotion at room temperature, or an acid wave with heat, and never both.
Can high-porosity hair be permed?
Sometimes, and often not. Where the porosity comes from weathering, sun or heat and the elasticity still holds, a milder chemistry on a shorter time can work. Where it comes from a hydroxide relaxer it is refused outright, because one sulphur has been removed permanently. Where it comes from bleach the answer is usually no, because the bonds themselves are gone — that is the default, and how much lightener, how long ago and how much has grown out are judged on the hair in front of me rather than read off a page.
Is high porosity the same as damaged hair?
Close, but not the same, and the difference decides what can be done. Porosity describes how the cuticle and its lipid layer are behaving; damage describes what has happened to the cortex underneath. Hair can be porous from weathering while its disulphide bonds remain largely intact, and that hair can often be processed with care. Hair that is porous because it was bleached has lost the bonds themselves. That is why your stylist tests elasticity as well: the first reading tells them how fast the chemical goes in, the second tells them whether there is anything for it to work with.
Why do my roots and my ends behave so differently?
Because they are different ages. Your roots are a few months old and still carry their lipid layer; your ends may be three years old and have been through colour, heat, sun and every wash in between. One lotion at one strength across both finishes the ends while the roots have barely started, which is why multi-zone application exists and why a good perm takes longer than a quick one.