Porosity: the key to finally choosing the right products for your curls
How to recognize it so you can stop guessing and start truly understanding your curly or coily hair.
How many times have you bought a hair product hyped as a miracle, only to end up with dull, weighed-down, or still-dry hair? That's not a coincidence, and more importantly, it's not your fault.
In most cases, the key lies in a factor people forget to look at: your hair's porosity. Once you understand that, you finally understand why a product works wonders for your friend and does absolutely nothing for your curls.
What exactly is porosity?
Porosity is simply your hair's ability to absorb and hold onto moisture. It depends on the condition of the cuticle, the thin outer layer made up of tiny scales that covers each strand, much like the shingles on a roof.
When the cuticles lie flat against each other, water and product ingredients have a hard time getting in. But once they do get in, they stay put: that's low-porosity hair. On the flip side, when the cuticles are lifted or damaged, moisture gets in easily, but it leaves just as fast. That's high-porosity hair. It's this balance between absorption and retention that determines your porosity type.
Why it matters even more for curly and coily hair
On a smooth, cylindrical strand, scalp sebum naturally travels down the hair and moisturizes it from root to tip. On a curly or coily strand, the spiral or zigzag structure creates multiple twists that slow this migration down, sometimes stopping it altogether.
That's why textured hair is naturally drier, regardless of its starting porosity. It's also why tailoring your routine to your porosity matters so much: two people with similar curls can follow the exact same routine and get completely different results.
Low, medium, high porosity: what's the difference?
Low porosity
The cuticles are tight and closed. Water and products have a hard time getting in, but once they do, your hair holds onto moisture well. It dries slowly, and can build up product residue if you use formulas that are too rich.
The happy medium
The cuticles hold together well while still letting in a moderate amount of moisture. This hair type generally needs less upkeep to stay hydrated and holds its definition more easily.
High porosity
The cuticles are lifted or damaged, often from heat, chemical treatments, or repeated manipulation. Moisture gets in fast, but it leaves just as fast, which makes hair more prone to frizz and breakage.
Good to know: your porosity isn't set in stone. There's a genetic component, but it also changes with damage that builds up over time (heat, chemical processing, friction). High porosity is often a sign of a weakened hair fiber rather than a fixed trait.
The water glass test: is it actually reliable?
The famous water glass test is everywhere: drop a clean strand of hair into water, and if it floats, porosity is supposedly low; if it sinks, porosity is supposedly high. It's popular, but this test isn't recognized by trichologists or taught in cosmetology. It's never been scientifically validated.
In reality, clean, dry hair initially floats because of water's surface tension, a physical phenomenon that has nothing to do with the strand's actual absorption. Product residue, natural oils, or even the hair's diameter can completely throw off the result.
A more reliable method: watch how your hair actually behaves day to day.
Low porosity takes a long time to dry. High porosity dries almost right away.
If water beads up on the surface or products tend to build up, your porosity is probably low. If your hair absorbs almost instantly but dries out just as fast, it's probably high.
Smooth leans toward medium porosity. Dense or coarse leans toward low porosity. Rough, with a slightly bumpy feel, leans toward high porosity.
None of these signs is perfect on its own, but tracking them together over a few weeks gives you a much more reliable picture than a one-time test.
How to adapt your routine to your porosity
Understanding your porosity isn't just a scientific curiosity. It's what explains why your routine should be built around you, not copied from someone else's.
Low-porosity hair often needs a bit of heat to help products penetrate, along with lighter textures to avoid buildup. High-porosity hair, on the other hand, needs frequent hydration, along with a step that helps lock that moisture in for longer.
And porosity is just one piece of the puzzle. It interacts with your hair's texture, density, and elasticity. It's the combination of all these factors that really lets you understand what your curls or coils need.
No matter your porosity, a regular hydrating mask and a curl-defining cream that doesn't leave curls stiff remain must-haves for keeping your curls soft and well hydrated.
In summary
Your porosity determines how your hair absorbs and holds onto moisture, an especially important factor when you have curly or coily hair, which is naturally more prone to dryness. Rather than relying on an unvalidated at-home test, take the time to observe your hair over the weeks. Knowing your hair is already the first step to taking good care of it.
Gisèle xx
