Hair Porosity Explained: Low, High and Why It Matters
Hair porosity describes how readily your hair takes in and holds onto water. Low porosity hair has a tightly closed cuticle, so products tend to sit on top. High porosity hair has a raised or damaged cuticle, so it absorbs quickly and loses moisture just as fast. Knowing which you have changes how you should apply almost everything.
Porosity is the most useful hair concept most people have never had explained properly and it's the reason two people can use the identical product and get opposite results.
It's also surrounded by a test that doesn't work. We'll get to that.
What Porosity Actually Means
Each strand of hair is wrapped in a cuticle, overlapping scales, a bit like roof tiles. How tightly those scales lie determines how easily water and product get in, and how easily they get back out.
Low porosity means tightly packed scales. Water beads on the surface, hair takes a long time to get properly wet and a long time to dry, and products have a tendency to sit on top rather than absorb.
High porosity means raised or gapped scales, usually from colouring, bleaching, heat or general wear, though some people are naturally higher porosity. Water goes in fast and leaves just as fast, so hair soaks up product and still feels dry hours later.
Medium porosity sits between the two and is the easiest to look after, which is why it gets discussed least.
Porosity is partly genetic and partly earned. Chemical processing and heat raise it permanently, see our guide to why hair breaks and how to reduce it for what's reversible and what isn't.
The Float Test Doesn't Work
You'll be told to drop a shed hair into a glass of water: sinks means high porosity, floats means low.
Don't rely on it. Whether a hair floats depends mostly on surface tension, on any product residue or natural oil on the strand, and on how you dropped it in. Clean hair floats regardless of porosity. Oily hair sinks regardless of porosity. The test has no meaningful basis.
It persists because it's visual and satisfying, which is a poor standard of evidence for anything.
What actually tells you more is how your hair behaves day to day:
| Sign | Low porosity | High porosity |
|---|---|---|
| Getting hair wet | Water beads, takes a while to saturate | Soaks instantly |
| Drying time | Slow often hours | Fast |
| Product behaviour | Sits on top, builds up | Absorbs fast, seems to vanish |
| After conditioning | Can feel coated or heavy | Feels dry again within hours |
| Typical cause | Mostly genetic | Usually colour, bleach or heat |
Looking After Low Porosity Hair
The problem is getting anything in, not keeping it there.
- Use warmth. Apply treatments to warm, damp hair, or wrap it in a towel afterwards. Gentle heat helps the cuticle lift slightly
- Go lighter. Heavy butters and thick creams sit on the surface and build up. Lightweight oils absorb better grape seed and camellia are among the lightest
- Less product, applied more evenly. Low porosity hair needs less than you think, worked through properly
- Clarify occasionally. Build-up is the main enemy, and a deeper cleanse every few weeks resets it
- Give treatments time. Fifteen minutes isn't enough. Overnight is better
Looking After High Porosity Hair
The opposite problem: everything goes in, nothing stays.
- Layer and seal. Hydrate first, then apply something on top to slow the loss. This is the single most useful habit for high porosity hair
- Protein can help in moderation. Protein treatments temporarily fill gaps in a damaged cuticle. Too often and hair turns brittle, so fortnightly to monthly rather than every wash
- Reduce heat. Every styling session raises porosity further. Lower settings, less often
- Cool final rinse. Modest effect, costs nothing, helps the cuticle lie flatter
- Protect from friction. A smoother pillowcase and looser ties reduce the mechanical wear that lifts the cuticle
What Porosity Doesn't Determine
Being clear, because porosity gets overextended online.
- It isn't the same as hair thickness or density. Fine hair can be low porosity; thick hair can be high. They're unrelated properties
- It doesn't dictate your curl pattern, though the two are often discussed together
- It won't explain hair loss. Shedding is a different matter entirely if it's sudden, patchy or rapid, see a GP or dermatologist
- It isn't permanent in one direction. You can't lower porosity back down, but you can stop raising it
Frequently Asked Questions
How do I test my hair porosity at home?
Observe rather than test. Note how long your hair takes to get properly wet, how long it takes to dry, and whether products sit on top or disappear. That behaviour tells you far more than the float test, which mostly measures surface tension and product residue.
Can I change my hair's porosity?
Only in one direction, unfortunately. Heat, bleach and chemical processing raise porosity permanently by damaging the cuticle. You can't close it back down, but you can stop the damage progressing and manage the hair you have with sealing and gentler handling.
Is low or high porosity better?
Neither they're just different, and each has its own frustrations. Low porosity hair resists build-up problems but is hard to treat. High porosity hair takes treatment easily but won't hold it. Medium porosity is the easiest to manage, which is why nobody talks about it.
Does porosity affect which oil I should use?
Yes, meaningfully. Low porosity hair does better with lightweight oils that can actually penetrate heavy ones sit on the surface and build up. High porosity hair can handle richer oils, since the priority is sealing moisture in rather than getting it there.
Can different parts of my hair have different porosity?
Very commonly, yes. The ends are older and have had more heat, washing and friction than hair near the scalp, so they're usually higher porosity. That's why ends often feel dry while roots feel fine, and why it's worth treating them differently.
The Takeaway
Porosity isn't a hair type you're assigned it's a description of how your cuticle is behaving right now, and it explains most of the confusion around why products work for some people and not others.
Skip the float test. Watch how your hair dries and how it responds to product. Then adjust: low porosity needs lighter products, warmth and time. High porosity needs layering, sealing and less heat.
For more on the mechanics, see our guides to hair oils and how to use them and the hair growth cycle.
Watch how it dries. Adjust from there.
Individual results may vary.
