In simple terms, porosity translates to how easily your hair absorbs moisture. Your hair can either be high porosity (easily absorbs moisture) or low porosity (doesn’t easily absorb moisture). “Curly hair is more porous than straight hair by nature,” Wilkerson explains. “Given that our hair is more porous, it also makes it more prone to damage.”
Chemical treatments (like keratin straighteners, relaxers, and permanent hair color) change the hair on a chemical level, damaging the outer layer of the shaft and making the hair more porous. But even if you’ve skipped all those treatments, your daily routine could effect your porosity. “Excessive manipulation and brushing of the hair can also remove the outer protective layer over time, causing strands to be more porous,” says Wilkerson.
So, how do you know whether your hair has high or low porosity? If you frequently heat style or color your hair, you can safely assume that your porosity is high. If it takes a long time for your hair to get wet (or dry), your porosity is probably low.
You can also try the “float test,” which is popular among naturalistas on YouTube. Place a strand of product-free hair in a clear cup of water and observe. Does your hair sink? If so, that’s a sign that your cuticles are lifted, which means your porosity is high. Did your hair float to the top and stay there? Then you’re dealing with cuticles that are tightly sealed, leaving you with low porosity curls. If your strands fall somewhere in the middle, you can consider your porosity normal.