Nine out of ten guides tell you to drop a hair in a glass of water. That test is close to useless, and there is published science explaining why.
Hair porosity is how easily water gets into your hair and how fast it leaks back out. Get it right and your products finally work. Get it wrong and you keep buying oils that just sit on top.
This guide gives you three tests that actually work, the water problem that quietly ruins most porosity results, and a plain routine for each type. No fluff. No myths repeated from other blogs.
Fastest answer: mist clean dry hair with water. Beads up means low porosity. Vanishes instantly means high porosity. Soaks in within a few seconds means medium.
Key takeaways
- Porosity is a property of the hair strand, not the follicle in your scalp.
- The float test is unreliable. The mist test and the dry time test are far better.
- High porosity is usually damage. A single bleach can strip over 80% of the hair's natural protective lipid layer.
- Hard water is common, and limescale on the strand fakes a low porosity result.
- Low porosity needs light products and warmth. High porosity needs sealing and protein.
- Roots and ends often have different porosity. That is normal.
On this page
- What hair porosity actually is
- Why the float test fails
- The 3 tests that actually work
- The 5 porosity grades stylists use
- Hard water: the hidden porosity faker
- Low porosity routine
- High porosity routine
- Mixed porosity
- Porosity and protein
- Your 7 day reset
- FAQs
What hair porosity actually is
Porosity lives in the cuticle. The cuticle is your hair's outer layer. It is made of flat cells that overlap like roof tiles.
- Tiles flat and sealed = low porosity. Water struggles to get in.
- Tiles slightly raised = medium porosity. Normal in, normal out.
- Tiles lifted or chipped = high porosity. Water rushes in and rushes back out.
Let us correct a myth you will find on page one of Google
Several popular pages say porosity is set by the width of your hair follicle. That is wrong. The follicle is the pocket in your scalp that grows the hair. It has nothing to do with how the finished strand absorbs water.
Porosity happens on the strand, not in the scalp. If a guide confuses those two things, be careful with the rest of its advice.
The bit almost nobody explains: the F layer
Healthy hair carries a thin, greasy coating on the outside of the cuticle. Scientists call it the F layer. Its main ingredient is a fatty acid called 18-MEA.
This layer is why virgin hair repels water. Strip it and the same hair suddenly drinks water like a sponge.
Here is the number that explains most high porosity hair. More than 80% of the 18-MEA layer can be removed by a single bleaching treatment (PMC12352994). Research also shows repeated shampooing and sun exposure strip it further over time (PubMed 21635851).
Translation: high porosity is usually earned, not inherited. One salon appointment can create it.
Honest note: low, medium and high porosity is a hairdressing shorthand, not a formal medical grade. Labs measure it with contact angle and water uptake equipment. The three bucket system is still useful, but treat it as a guide to behaviour, not a diagnosis.
Why the float test fails (and what the top pages get wrong)
We read the pages currently ranking for this topic. Almost every one leads with the float test. Drop a hair in water, wait, judge.
Here is why that glass lies to you.
| Problem | What it does to your result |
|---|---|
| Surface tension | A single strand weighs almost nothing. The water skin holds it up regardless of porosity. |
| Air bubbles | Tiny bubbles cling to the strand and float damaged hair. |
| Silicone or oil residue | Makes high porosity hair float. False low porosity reading. |
| Limescale on the strand | Mineral coating changes how the hair behaves in water. |
| Timing | Almost any hair sinks eventually. Wait too long and everyone is high porosity. |
| How you drop it | Laid gently it floats. Pushed under it stays under. |
Our position: use the float test as a weak hint only. If you insist, use hair pulled from a brush after a clarifying wash, and read it at exactly four minutes.
What we tested: we ran the float test with six people in the Replenhair studio. We took three strands from the same head and dropped them in the same glass. We got three different answers. That is the day we stopped recommending it on its own.
The 3 tests that actually work
Rules first. These only work on freshly washed hair with zero product on it. Product residue breaks every test below.
Test 1: The mist test (10 seconds)
- Take a dry, clean section.
- Mist it once with plain water from a spray bottle.
- Watch what the water does.
- Beads sit on top and roll off = low porosity
- Soaks in within a few seconds = medium porosity
- Disappears instantly, section looks damp all over = high porosity
This is the closest test to real life, because it copies exactly what happens when you apply a product.
Test 2: The dry time test (most reliable)
Wash. Squeeze out water gently. Apply nothing. Air dry and watch the clock.
| Air dry time | Porosity | Why |
|---|---|---|
| Over 3 hours, still damp for ages | Low | Water is sitting on the surface, not inside |
| 1 to 3 hours | Medium | Balanced cuticle |
| Under 1 hour, feels rough fast | High | Moisture escapes through gaps |
Compare yourself to yourself. Thick or long hair always takes longer, so do not judge against a friend.
Test 3: The slide test (no water needed)
Hold one strand by the tip. Slide two fingers up towards the root.
- Slick and smooth = low porosity
- Slight texture = medium porosity
- Bumpy and catchy = high porosity
Those bumps are lifted cuticle scales. You are feeling the damage with your fingertips.
Score it
- Two or three tests agree = that is your porosity
- Tests disagree = you likely have mixed porosity, covered below
- All three say low, but your hair also feels rough = suspect limescale, clarify and retest
The 5 porosity grades stylists actually use
Your colourist does not think in three buckets. The American Board of Certified Hair Colorists uses five grades. Knowing yours makes salon conversations much easier.
| Grade | Hair history | Maps to |
|---|---|---|
| 1 | Virgin hair, almost no damage. Rare. | Low |
| 2 | Virgin hair with normal sun and weather wear. Most people. | Low |
| 3 | Coloured up to about 5 shades lighter. | Medium |
| 4 | Bleached or lifted around 7 shades. Needs sealing and protein. | High |
| 5 | Gummy when wet, snaps easily. Cuticle effectively gone. | High |
Be straight with yourself about grade 5. If your hair stretches like chewing gum when wet and then breaks, no product fixes it. Cutting is the only answer. We would rather tell you that than sell you an oil.
Hard water: the hidden porosity faker
This is the section almost every other guide skips, and it changes test results more than anything else on this page.
Hard water carries dissolved calcium and magnesium. Those minerals settle on the cuticle and build a film. That film makes water bead on the surface, so your hair behaves exactly like low porosity hair even when it is not.
| Your water | Signs | What to do before testing |
|---|---|---|
| Very hard (above 250 mg/L) | Heavy limescale on taps and kettle, shampoo barely lathers | Always clarify first. Your result is otherwise unreliable. |
| Hard (150 to 250 mg/L) | Some scale, hair feels dull and stiff | Clarify monthly, then test. |
| Soft (below 150 mg/L) | No scale, products lather easily | Test results are usually accurate first time. |
Does hard water actually damage hair? Be careful here, because the evidence is genuinely split.
- A 2013 study in the International Journal of Trichology found no significant difference in tensile strength or elasticity between hair soaked in hard water and distilled water (PMID 24574692).
- A 2018 study in the same journal found hard water did reduce hair strength and increase breakage (PMID 30034190).
- Separate work confirms calcium and magnesium do build up in the cuticle and stiffen the fibre.
Sensible reading: hard water is unlikely to cause hair loss. It very likely causes buildup, dullness, stiffness and a fake low porosity reading. Clarify monthly and stop worrying about it.
Practical fix: one clarifying wash a month with Rice Water Shampoo, a shower filter if your water is very hard, and a final cool rinse.
Behaviour check: confirm your result
| Everyday sign | Low porosity | High porosity |
|---|---|---|
| Products | Sit on top, feel greasy | Soak in, gone by lunchtime |
| In the shower | Takes ages to get properly wet | Soaked in seconds |
| Salon colour | Slow to take, fades slowly | Grabs fast, fades fast |
| Humid weather | Usually fine | Instant frizz |
| Buildup | Constant battle | Rare |
| Tangles | Fewer | Constant, worst when wet |
Low porosity hair: the routine
Your real problem is not dryness. It is rejection. The door is shut and your products cannot get in.
Five rules
- Go light. Water based sprays and thin oils only.
- Use warmth. Apply to damp hair straight after a warm shower. Gentle heat helps absorption.
- Halve the amount. Then layer if you need more.
- Clarify monthly. Buildup is your number one enemy.
- Go easy on protein. Low porosity hair overloads quickly and turns stiff.
What to use
- Rosemary Rice Water Moisturising Spray. Water based and light enough to absorb instead of coating.
- Aloe Rice Water Moisturiser. Aloe is a humectant, so it draws water in rather than sealing it out.
- Jojoba Oil. Technically a liquid wax ester and very close in structure to your own scalp sebum. Use two or three drops, no more.
- Rice Water Shampoo for the monthly reset.
Skip: thick butters, daily heavy oiling, layering four products at once.
High porosity hair: the routine
Your real problem is not absorption. It is escape. Water walks straight in and straight back out.
Five rules
- Always seal. Water first, then cream, then oil. Never water on its own.
- Go richer. Heavy oils are your friend here.
- Protein helps. Gaps in the cuticle are exactly what protein temporarily fills.
- Cool rinse. Helps the cuticle lie flatter.
- Stop the cause. Bleach, straighteners and rough towels created this.
What to use
- Coconut Rice Oil. Worth knowing why. In a controlled study comparing coconut, mineral and sunflower oils, coconut oil was the only one that meaningfully reduced protein loss from both damaged and undamaged hair (PMID 12715094). Its lauric acid is small and straight enough to get inside the shaft.
- Batana Rice Oil. Rich and heavy, built for sealing. Be aware there are no published human trials on batana specifically, so judge it as a good sealing oil rather than a miracle.
- Argan Oil Hair Treatment. Argan mostly smooths the surface rather than penetrating deeply. That is exactly what rough, split ends need.
- Argan Rice Water Moisturiser as your water step before the oil.
Skip: water only refreshing, terry towels, daily straighteners, alcohol heavy sprays.
Medium porosity: protect what you have
- Balanced routine, no extremes
- Deep condition every two weeks
- Protein now and then, not weekly
- Heat protection every single time
Good picks: Coconut Rice Water Moisturising Spray and Super Seed Regrowth Hair Oil.
Mixed porosity: the one nobody warns you about
Roots feel one way, ends feel another. That is not confusion. That is normal.
Your ends are years older. They have survived sun, heat, brushing and hundreds of washes. Your roots are brand new. Same head, two different porosities.
- Treat roots as low porosity. Light spray only.
- Treat ends as high porosity. Seal with oil.
- Apply oil from mid length down. Never at the roots.
- Trim regularly. It is the only permanent fix for the worst ends.
What raises and lowers porosity
Raises it:
- Bleach and permanent colour (the big one)
- Relaxers and perms
- Heat styling above 180C, or 356F
- Repeated harsh cleansing
- Sun, chlorine and sea salt
- Rough towel drying and aggressive brushing
Lowers it, or hides it:
- Oils and silicones (cosmetic and temporary)
- Protein treatments (temporary fill)
- Cutting off damaged length (the only permanent one)
The honest bit: nothing regrows cuticle scales. No oil, no mask, no bond builder rebuilds what bleach removed. Good products smooth, fill, coat and protect so hair behaves better and breaks less. Anyone promising permanent repair in a bottle is selling you a story.
Porosity and protein: the rule that ends the confusion
- High porosity = more gaps = protein usually helps
- Low porosity = fewer gaps = protein overloads easily
- Overload feels like straw, stiffness, and snapping instead of stretching
Rice water sits right in the middle of this debate because of its amino acid content. If you are low porosity and rice water made your hair crunchy, that is real. Read can rice water damage hair and fermented vs plain rice water before you go further.
Your 7 day porosity reset
- Day 1 morning. Clarifying wash. No products afterwards.
- Day 1 evening. Run all three tests. Write the results down.
- Day 2. Pick your lane. Light and layered, or rich and sealed.
- Day 3. Add one new product. One only.
- Day 4. Judge how hair feels 12 hours after applying, not 12 minutes.
- Day 5. Change the amount before you change the product.
- Day 7. Repeat the mist test. Compare with day one.
Most people fail at step 4. They change five things at once and learn nothing.
Six mistakes we see constantly
- Testing on product coated hair. Every result will be wrong.
- Trusting the float test alone. See above.
- Heavy oil on low porosity hair. It never absorbs. It just attracts dirt.
- Water only refresh on high porosity hair. The water evaporates and takes moisture with it.
- Oiling soaking wet low porosity hair. Damp, not dripping.
- Never retesting. Porosity shifts after colour, after summer, after a big trim.
Match your porosity to a product
| Porosity | Moisture step | Seal step |
|---|---|---|
| Low | Rosemary Rice Water Spray | Jojoba Oil, 2 to 3 drops |
| Medium | Coconut Rice Water Spray | Super Seed Regrowth Oil |
| High | Argan Rice Water Moisturiser | Coconut Rice Oil or Batana Rice Oil |
| Mixed | Light spray at roots | Rich oil on ends only |
| Hard water area | Clarify first | Rice Water Shampoo monthly |
Keep reading
- Rice water for hair: the full guide
- Why your hair is dry
- Protein treatments explained
- How to use argan oil for hair growth
- Coconut rice water for curly hair
- Batana oil benefits
- Castor oil for hair
- Chlorine damage and your hair
- Is mineral oil good or bad for hair
Frequently asked questions
What is the most accurate hair porosity test at home?
The dry time test. Wash your hair, apply nothing, and time how long it takes to air dry. Under one hour suggests high porosity. Over three hours suggests low porosity. Confirm it with the mist test.
Is the float test accurate?
Not reliably. A single strand is affected by surface tension, air bubbles, product residue and limescale far more than by porosity itself. Treat it as a weak hint, not an answer.
How long should I wait during the float test?
About four minutes. Wait much longer and almost any strand sinks, which gives a false high porosity reading.
How do I test hair porosity without water?
Use the slide test. Run two fingers up a single strand from tip to root. Bumpy and catchy means high porosity. Slick and smooth means low porosity.
Can hair porosity change?
Yes. It rises with bleaching, colouring, heat, sun and chlorine. It only drops permanently when you cut the damaged length off. Products improve how hair behaves but cannot rebuild cuticle scales.
Is high porosity hair damaged hair?
Usually yes. Research shows more than 80% of the hair's natural protective 18-MEA lipid layer can be removed by a single bleaching treatment, which is why colour treated hair so often behaves as high porosity.
Does hard water affect my porosity test?
Yes. Limescale coats the strand and mimics low porosity, so water beads on the surface even when your cuticle is not sealed. Clarify first, then test.
Does hard water damage hair?
The evidence is mixed. A 2013 study found no significant change in hair strength or elasticity, while a 2018 study found hard water did reduce strength and increase breakage. What is clearer is that minerals build up on the cuticle and cause stiffness, dullness and buildup.
What oils are best for low porosity hair?
Light oils that absorb rather than coat. Jojoba is the standout because it is a wax ester structurally close to your own scalp sebum. Use two or three drops on damp hair.
What oils are best for high porosity hair?
Richer sealing oils such as coconut, batana, castor and argan. Coconut oil has the strongest evidence behind it, as it was the only oil in a published comparison against mineral and sunflower oil to significantly reduce protein loss from hair.
Does low porosity hair need protein?
Rarely, and only in small amounts. Low porosity hair overloads easily, which leaves it stiff and prone to snapping instead of stretching.
Why does my hair feel dry even though I moisturise every day?
Two likely reasons. Either you are low porosity and the product never gets in, or you are high porosity and the moisture escapes because you never seal it.
Can my roots and ends have different porosity?
Very commonly, yes. Ends are older and more weathered. Treat roots light and ends rich.
Is porosity determined by my hair follicle size?
No. That is a common error online. Porosity is a property of the cuticle on the hair strand itself. The follicle in your scalp does not control it.
How often should I retest my porosity?
Every three to six months, and always after colouring, a big trim, or a summer of sun and swimming.
Does rice water suit every porosity type?
Not always. Low porosity hair can react to the amino acid content and feel stiff. Start with a diluted, plain rice water rather than a long fermented one.
Is low porosity or high porosity better?
Neither. Low porosity resists moisture. High porosity loses it. Both are easy to manage once your products match the behaviour.
About the author
Aditya Singh is the founder of Replenhair, a haircare brand formulating rice water and rosemary based products. This guide was fact checked against peer reviewed cosmetic science literature, including Gavazzoni Dias MF, "Hair Cosmetics: An Overview", Int J Trichology 2015;7(1):2-15 (PMID 25878443); Rele AS and Mohile RB, J Cosmet Sci 2003;54(2):175-192 (PMID 12715094); Srinivasan G et al., Int J Trichology 2013;5(3):137-139 (PMID 24574692); and Luqman MW et al., Int J Trichology 2018;10(3):113-117 (PMID 30034190).
Last reviewed: July 2026. This article is general information, not medical advice. If you have sudden hair loss, scalp pain or a scalp condition, please speak to a doctor or a dermatologist.