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Curl type tells you the shape of your hair. Porosity tells you how it behaves, and it is the better guide to what you should buy. Two people with identical ringlets can have opposite experiences with the same product, and porosity is usually the reason.
What porosity is
Each strand of hair is covered in a layer of overlapping scales called the cuticle, arranged like shingles on a roof. Porosity describes how tightly those scales lie.
- Low porosity hair has a flat, tightly closed cuticle. Water and products have trouble getting in. Once moisture is inside, it stays.
- High porosity hair has a raised or damaged cuticle with gaps in it. Moisture goes in easily and leaves just as fast.
- Medium porosity hair sits between the two and is the easiest to look after.
Porosity is partly inherited and partly earned. Bleach, hair color, heat styling and sun all lift the cuticle and push hair toward the high end. It is also common to have more porous ends than roots, simply because the ends are older.
How to tell which you have
You may have seen the float test, in which a strand is dropped into a glass of water to see whether it sinks. It is not reliable. Surface tension, the oil on the strand and any product residue all change the result.
Observation works better. Ask yourself three questions.
| Question | Low porosity | High porosity |
|---|---|---|
| How long does your hair take to get fully wet? | A long time; water beads on the surface | Almost instantly |
| How long does it take to air dry? | Many hours | Quickly |
| What do products do? | Sit on top and feel greasy | Disappear, and the hair is dry again by evening |
If your answers fall in the middle, or split between columns, treat your hair as medium porosity.
Low porosity hair struggles to let moisture in. High porosity hair struggles to keep it.
Caring for low porosity hair
The aim is to get moisture past a closed cuticle without leaving a film on top of it.
- Choose light, water-based products. Thin lotions and milks absorb where thick butters will not.
- Use warmth. Apply deep conditioner and cover it with a shower cap for twenty minutes. Gentle heat helps the cuticle lift.
- Clarify regularly. Low porosity hair builds up quickly.
- Go easy on protein. Many people with low porosity hair find frequent protein treatments leave it stiff.
Caring for high porosity hair
Here the task is to fill the gaps and slow the escape.
- Layer. A leave-in, then a cream, then an oil or butter to seal. This is the thinking behind the well-known LOC and LCO layering methods.
- Use protein. Hydrolyzed proteins temporarily patch a damaged cuticle. We cover this in Protein and Moisture.
- Deep condition weekly.
- Reduce further damage. Lower the heat, and protect your hair at night.
The limits of the idea
Porosity is a useful model, not a diagnosis. Hair varies along its length and across the head, and no home test measures it precisely. Use it as a starting point. If your hair is thriving on products that are supposedly wrong for your porosity, your hair is right and the chart is wrong.