The hair porosity test: why the float test fails, and 3 checks that work
Porosity decides whether your products sink in or sit on top. The famous float test gets it wrong more often than it gets it right.
The short version
- Porosity is how easily water and product get into your hair — and how fast they leave.
- The float test is skewed by oils, product residue and surface tension. Don’t trust it.
- Watch how your hair wets, how long it takes to dry, and how product behaves. Those three tell you more.
- Bleach and heat permanently raise porosity. Your ends are almost always more porous than your roots.
Every strand of hair has a cuticle — overlapping scales, a bit like roof tiles. When they lie flat and tight, moisture has a hard time getting in (low porosity). When they’re raised or chipped, moisture rushes in and rushes out again (high porosity). Medium sits in between, and is the easiest to look after.
Why the float test is unreliable
You’ve seen it: drop a hair in a glass of water and see if it sinks. The idea is that porous hair absorbs water and sinks. In practice:
- Any oil, conditioner or styler residue on the strand makes it float, whatever its porosity.
- Surface tension holds a dry hair up for ages; a tap on the glass sinks almost anything.
- Shed hairs from a brush are old ends — they don’t represent the hair growing from your scalp.
Cosmetic chemists have been grumbling about it for years. Use it for fun, not for buying products.
Three checks that actually work
| Check | Low porosity | Medium | High porosity |
|---|---|---|---|
| Wetting — how fast does hair get soaked in the shower? | Water beads and runs off; takes a minute or more | Soaks through in under a minute | Soaked almost instantly |
| Drying — air-dry time with no product | Hours. Still damp at bedtime | A few hours | Fast — often under an hour |
| Product — what happens to a leave-in? | Sits on top, feels greasy or filmy | Absorbs, holds | Disappears, hair is thirsty again by evening |
If two of the three point the same way, that’s your answer. If you get a mix, you’re probably medium with porous ends — the most common result of all.
How does your hair take product?
What each porosity needs
Low porosity
Lightweight, water-based products. Apply leave-in to soaking-wet hair with warm hands so the cuticle is as open as it gets. Heat during deep conditioning helps. Butters and heavy oils just sit there. Full guide: low porosity curly hair routine.
Medium porosity
Lucky you. A normal rinse-out, a leave-in and a styler. Watch the ends, which are usually more porous than the rest.
High porosity
Richer conditioners, regular deep conditioning, and something to seal moisture in (a cream or a light oil). Some protein helps patch the gaps. Full guide: high porosity curly hair routine.
How Coil uses your porosity
Porosity is one of the inputs that changes your daily plan, not just a label on your profile. On a wash day, high porosity (or bleached hair) gets “Deep condition, 10 min” instead of a quick rinse-out, and low porosity gets “Leave-in on soaking hair, warm hands” so product actually goes in.
Wash day
- Co-wash & detanglewash
- Condition & finger-combcondition
- Leave-in on soaking hair, warm handscondition
- Diffuse on low heatstyle
Questions people ask
Can hair porosity change?
Yes, mostly upward. Bleach, colour, heat and sun damage raise porosity, and it doesn’t reverse. New growth comes in at your natural porosity, so you can have low-porosity roots and high-porosity ends.
Is low porosity hair healthy?
Usually, yes — a tight cuticle means it is well protected. It is just harder to moisturise, and prone to build-up.
Do I need protein if I have high porosity hair?
Often, in moderation. Protein temporarily fills gaps in the cuticle. Too much makes hair stiff and brittle, so balance it with moisture.