Diagnosis

Hair Porosity Test

Answer eight questions about how your hair drinks water, dries and holds color, and get its porosity with the developer, level and timing changes to make before you mix.

Free, no sign-up. Runs in your browser. Reviewed 2026-09-04.

Eight questions

0 of 8 answered. Five give a reading, all eight give the most confident one.

1. In the shower, how long before the hair is wet right through?
2. Left alone, how long does it take to air-dry?
3. What do conditioners and leave-in products do on it?
4. Slide two fingers up a dry strand toward the scalp. How does it feel?
5. What chemical services has this hair had?
6. When it has been colored, how did the color behave?

Skip this one if the hair has never been colored.

7. How much frizz and breakage do you see?
8. How often does it see heat: irons, wands, a hot dryer?

Your porosity

Answer the questions and your porosity appears here. Five answers give a reading; all eight give the most confident one.

In one line

Porosity is how easily the cuticle lets water and color in and out. Low porosity resists color and then holds it; high porosity grabs it fast and fades it fast. The finger test beats the float test: a glass of water measures product build-up and surface tension, which is a different thing from the cuticle.

Start with your fingers, not a glass

Take one clean, dry strand, still growing, from near the crown. Hold the end loosely and slide two fingers up toward the scalp, against the grain. Go slowly. You are feeling for the cuticle, the overlapping scales that wrap every hair like roof tiles, and this lifts their edges just enough to read them.

Smooth and slippery: the tiles lie flat and tight, low porosity. A faint dry texture, like fine thread: they lift a little and settle back, medium. Rough and bumpy, catching on your finger: raised, chipped or gone, high, usually because the hair has been through bleach, sun, heat or simply years.

I keep a bleached strand taped to an index card, and when a new assistant cannot feel the difference I hand her the card with one of mine and make her close her eyes. (Every client tells me her hair is dry. Every single one. It says nothing about the cuticle.) But one strand can lie, so try three places, then answer the eight questions above.

Put the glass of water away

The float test is everywhere and it is mostly wrong. Supposedly high porosity sinks and low floats. What decides it is surface tension and whatever coats the hair: conditioner, oil or dry shampoo keeps a strand afloat, and a clarified one pushed under with a fingertip sinks whether it is virgin or bleached. The glass measures build-up, plus how gently you let go.

Low porosity: the hair that says no

How it feels

Smooth to the point of slippery. Water beads and rolls off before the hair gives in, it takes hours to air-dry, sometimes still damp at bedtime, and conditioner sits on top so you rinse and rinse and it still feels coated. Glossy and strong, and it wants nothing you are offering.

What it does to color

The dye has to get past that shut door, so this hair resists. Color comes out a shade lighter and a touch cooler than the swatch, gray looks translucent at first, and everything takes its full time. Once the pigment is in it stays for weeks, so the fade you correct elsewhere mostly does not come.

What to change in the formula

Process the full manufacturer time. Use 20 volume even for deposit on stubborn hair; 10 volume struggles to lift the cuticle enough for pigment to settle. Warm the hair (a hood, or a warm towel over the cap) or pre-soften resistant gray first. I learned the warmth part the slow way: a woman whose hair squeaked when combed dry, whose color slid off twice, two rebooks at my cost, before I put her under the hood for the extra ten minutes. I have never liked pre-softening; in my chair warmth and the extra minutes do the job, though good colorists would argue. Then go half a level warmer than instinct says, since it will not grab cool: a 7.1 often reads as a plain 7N, so lean natural or gold over ash.

Medium porosity: the hair the instructions were written for

How it feels

A faint texture, nothing you would call rough. Water soaks in after a few seconds, the hair dries in about an hour, products absorb and leave it soft.

What it does to color

This is the baseline: the swatch is roughly what you get and the fade is the one the brand tested.

What to change in the formula

Nothing much. Ratio by weight, standard developer (10 for demi and toner, 20 for deposit and gray, 30 for lift), standard timing; the processing time calculator is written for this hair. Your one adjustment is the ends, always a touch more porous: a few minutes after the roots.

High porosity: the hair that drinks and forgets

How it feels

Rough and catching, sometimes squeaky. Wet the instant it meets water, dry before the towel is down. Products vanish into it and it still feels thirsty, it frizzes in any weather, the ends split and snap.

What it does to color

Open cuticle, open door. It grabs color fast and grabs the dark, cool part hardest: a 7.1 can land as a muddy 6 with a green shadow. Nothing holds the pigment in, so it lets go just as fast: two or three washes and the brass is back. I toned a swimmer who had swum every morning that summer, and his ends drank the toner in three minutes flat while the mid-lengths were still deciding.

What to change in the formula

Everything comes down, the developer first.

  • 10 volume or a demi-permanent wherever the service allows (the toner selector assumes this).
  • Half a level to a full level lighter and warmer than the target.
  • Shorter processing, ends checked at the halfway mark.
  • A protein filler or equalizing spray first, so pigment lands evenly.
  • Ends last, and expect a faster fade whatever you do.

What the quiz cannot see is how uneven one head is. It gives one number, and a head lightened in pieces two summers running has stripes of every porosity; there I go by feel, and the filler goes wherever the fingers catch.

All three on one table

PorosityDeveloperProcessingFormula shift
Low20 vol even for deposit; 30 vol for liftFull time, plus 5 to 10 minutes with warmthHalf a level warmer; natural or gold over ash
Medium10 vol demi and toner; 20 vol deposit and gray; 30 vol liftManufacturer timeNone; ends a few minutes after roots
High10 vol or demi wherever possibleShorter; check early; ends lastHalf to one level lighter and warmer; filler first
One strand, two porositiesEvery strand is a timeline. The half inch at the scalp grew last month and has never met a bowl of anything: its cuticle is new and closed. The ends may be three years old, bleached, toned and ironed, their cuticle raised where it is not missing. One formula for one time under-processes the roots and over-grabs the ends. When the quiz flags a mixed result, treat the regrowth as low porosity and the lengths as high.

Test again after anything big

Porosity is a condition of the cuticle at the moment you touch it, and it changes in an afternoon. A full bleach, a relaxer, a keratin smoothing, a summer of salt water: each one chips the cuticle further and moves the answers above. Retest before any color you care about and always after a big chemical service, then strand test, and follow the manufacturer.

What people ask about porosity

How do I know if my hair is low or high porosity?

Slide two fingers up a dry strand toward the scalp. Smooth and slippery is low porosity, a faint dry texture is medium, rough or catching is high. Then watch what the hair does over a week: low porosity hair beads water and takes hours to dry, high porosity hair is wet the moment it meets water and dry again minutes later. The quiz above turns those signs into one score.

Is the hair porosity float test accurate?

Honestly, no. Whether a strand floats depends on surface tension and on whatever is coating it: conditioner, oil, dry shampoo and silicone all keep a hair afloat regardless of its cuticle. A clarified strand pushed under with a fingertip sinks whether it is virgin or bleached. Use your fingers and the way the hair wets and dries.

What developer should I use on high porosity hair?

The lowest that will do the job, which means 10 volume or a demi-permanent for deposit and toning because the cuticle is already open and does not need peroxide to force it, 20 volume only where you need gray coverage on the regrowth and kept off the porous lengths, a shorter processing time, and the ends checked early.

Why does low porosity hair not take hair dye?

The cuticle scales lie flat and tight, so the dye has to work harder to get underneath them. Color comes out lighter and cooler than the swatch and gray looks translucent. Process the full time, use 20 volume even for deposit, add a little warmth during processing and formulate half a level warmer, because this hair will not grab cool tones easily. The gray coverage calculator covers the resistant-gray side of that.

Should I use a protein filler before coloring high porosity hair?

Yes, when the hair is uneven or very porous. I skipped it once on a grown-out balayage because we were running late, and the lightened pieces came out visibly darker than the natural hair beside them, striped, and it took a second appointment to even out. A protein filler or equalizing spray fills the gaps in the damaged cuticle so pigment lands evenly; without it the color pools in the most porous spots, which is what causes dark patches and banding on lightened hair. Apply it to towel-dried hair as the product directs, then color with 10 volume or demi and put the ends on last.

Can hair be low porosity at the roots and high porosity at the ends?

Very often, and it is the most common reason one formula gives two results on one head. The roots grew in the last few weeks and have never been touched; the ends may be three years old and have seen bleach, sun and heat. Treat them as two heads of hair: 20 volume and full time on the regrowth, 10 volume or demi and a shorter time through the lengths, ends last. Porosity also changes with every big service, so retest before each color.

Keep going with these

Diagnosis Gray Coverage Calculator How much natural base to add, which developer to use and how long to process for your gray percentage. Formulation Developer to Color Mix Calculator Exact grams or ml of color and developer for any ratio, from a 10 g touch-up to a full bowl. Service & Timing Hair Dye Amount Calculator How many grams of color to mix for a root touch-up, regrowth or full head, by length and density.

Results are estimates built from standard colorimetry practice. Products differ by brand and hair differs by head, so always follow the manufacturer's instructions and strand test before a full application.