Hair porosity explained
Porosity describes how well your hair absorbs and holds moisture. It is one of the most useful things to understand about your hair, often more useful than curl pattern for choosing products.
Porosity refers to the state of your hair's cuticle, the overlapping scales that form the outer layer of each strand. When these scales lie flat and close together, moisture has difficulty getting in or out: this is low porosity. When they are raised or damaged, moisture absorbs quickly but escapes just as fast: this is high porosity.
Low porosity hair often feels resistant to moisture initially. Products can sit on the surface rather than absorbing. Heat (from a warm shower or a steamer) helps open the cuticle temporarily and allows products to penetrate more effectively.
High porosity hair, which can be genetic or caused by damage from heat, chemicals, or the environment, needs products that help seal moisture in. Heavier butters, oils, and film-forming ingredients are more effective for high-porosity hair.
Medium porosity is often the easiest to manage. The cuticle accepts and retains moisture without too much effort, and a wider range of products tend to work.