Porosity describes hair's ability to let water and actives in and out. It depends on the state of the cuticle: tightly closed scales and the fibre is barely permeable (low porosity), slightly ajar scales and exchanges happen well (medium porosity), lifted or missing scales and the fibre absorbs everything then loses everything (high porosity). It is the indicator that best explains why the same product transforms one head of hair and does nothing on another.
A warning right away: home tests give an indication, not a measurement. Porosity can only truly be measured in a laboratory. That is enough to guide a routine, not to deliver a verdict.
The 3 porosity profiles
| Profile | State of the cuticle | What you observe | The main need |
|---|---|---|---|
| Low | Tightly closed scales | Slow to wet, endless to dry, products that sit on the surface | Getting things in |
| Medium | Slightly ajar scales | Takes products well, dries in a reasonable time, holds a style | Maintaining |
| High | Lifted or chipped scales | Drinks water instantly, dries very fast, frizzes at the slightest humidity | Filling and sealing |
Two origins combine: a genetic part, curly and coily hair being naturally more porous because the spiral of the fibre mechanically prises the scales apart, and an acquired part, linked to bleaching, heat, UV and friction. The acquired part moves in both directions: that is what makes porosity worth tracking.
How to assess your porosity: 3 methods to cross-check
- Day-to-day observation. The most reliable of the three. Hair that is slow to wet and endless to dry points to low porosity. Hair that soaks up water instantly and air-dries in record time points to high porosity.
- Touch. Slide a hair between two fingers, from the ends towards the root. Perfectly smooth: closed scales. Rough or uneven: lifted scales.
- The glass of water. Drop a clean, naturally shed hair onto the surface of a glass of room-temperature water and watch for two to four minutes. Floats for a long time: low porosity. Sinks slowly: medium. Sinks quickly: high.
What the glass of water test is worth. It is the best known, and it is also the least reliable of the three. The result depends heavily on the surface tension of the water, on product or sebum residue on the hair, and on how you drop it in. It has never been scientifically validated. Use it as one clue among three, never on its own.
Test several areas: the ends are almost always more porous than the roots.
Low porosity: getting care in
Your hair shines naturally but seems impermeable, products sit on the surface and weigh it down. Your problem is not nourishing more, it is getting things in better.
- Gentle warmth while the product sits. A warm towel or a cap prises the scales slightly apart and noticeably improves absorption.
- Light textures. Mists, milks, fluid creams rather than thick butters that build up. The /REVEAL Mist is the format that suits.
- Small doses, rich products spaced out. One mask a week is more than enough.
- Watch for build-up. This profile clogs up quickly: a careful wash with a gentle base such as the /RESET Shampoo keeps the fibre receptive.
High porosity: fill, seal, protect
Your hair drinks up products without ever seeming satisfied, dries in twenty minutes and frizzes at the first hint of humidity. This is the profile of sensitised fibres, often after colouring or repeated heat, and the ground on which most signs of damaged hair appear.
- Fill. Proteins, hydrolysed keratin first among them, fill the gaps in the cuticle. The /REPAIR Mask once or twice a week is the backbone of the routine.
- Seal. A final cool-water rinse to tighten the scales, then a leave-in every time as a barrier.
- Protect. Moderate heat, gentle drying, a silk pillowcase. Every assault avoided is one gap fewer to fill.
The /REPAIR + /REVEAL Repair Duo covers this trio. Keep an eye on the balance, though: too much protein without moisture stiffens the fibre.
Medium porosity and special cases
Medium porosity is the balance the other two profiles are trying to reach. The mission is simple: keep it, with the 4-step routine at standard frequency and an eye on the things that damage hair.
- Mixed porosity is very common: barely porous roots, very porous older ends. Adapt zone by zone, light textures at the top, rich care concentrated on the lengths.
- Porosity changes. Reassess every two to three months, especially after a summer, a colouring or an intensive repair phase. Watching a hair go from "sinks immediately" to "sinks slowly" is still the clearest sign that your routine is working.
Porosity: the essentials
- Porosity describes how permeable the cuticle is, not how thick the hair is.
- Cross-check three clues: everyday drying, touch, glass of water.
- The glass of water test is not scientifically validated: it is a clue, not a verdict.
- Low porosity: get things in. High: fill and seal. Medium: maintain.
- The acquired part of porosity is corrected within two to three months of a suitable routine.
Frequently asked questions about hair porosity
Is the glass of water test reliable?
Partly. It gives an indication provided you use a clean, naturally shed hair, but it has no scientific validation and the result depends heavily on the surface tension of the water. Always cross-check it against touch and what you observe when drying.
Can you change your hair's porosity?
You cannot change the genetic part, but the acquired part moves in both directions: damage increases it, protein care and good habits gradually close the cuticle back down. Allow two to three months for a clear improvement.
Is curly hair necessarily very porous?
It is naturally more porous than straight hair, because the spiral of the fibre mechanically prises the scales apart, but every level exists. Assessing it is still essential.
High porosity and greasy hair, is that possible?
Yes: porosity concerns the fibre, sebum concerns the scalp. They are two independent subjects. A two-zone strategy is then called for, frequent gentle washes at the top, rich care on the lengths.
Which ingredients should you favour with high porosity?
Proteins that fill, hydrolysed keratin first and wheat proteins alongside, humectants that hold water such as Sodium PCA, and lipids that seal such as shea butter.
How often should you reassess?
Every two to three months, and always after a significant event: a summer in the sun, colouring, bleaching or the end of a repair course.
Sources
- Robbins C. R., Chemical and Physical Behavior of Human Hair, 5th edition, Springer, 2012, chapters on water sorption and cuticle structure.
- Gavazzoni Dias M. F. R., "Hair Cosmetics: An Overview", International Journal of Trichology, 2015.
Article written by the KERA NEXT editorial team. The tests described are common practical markers, with no value as scientific measurement. Individual results: the outcome may vary depending on the nature and condition of your hair.