The hair cuticle determines hair porosity. The cuticle is the protective outer layer of the hair made up of flat cells that overlap each other like the shingles on a roof.
Low Porosity Hair:
The cuticle is flat and tight, making it difficult for moisture to penetrate the cuticle, resulting in longer drying time and product buildup. It generally gets better results by avoiding heavy products and loves steam or heat when conditioning to allow for full moisture absorption. Hair tends to look healthy and shiny.
Medium (or normal) Porosity Hair:
The cuticle is slightly raised, allowing some moisture to penetrate the cuticle, resulting more elasticity and manageability. Moisture doesn’t escape very easily and styles tend to last longer. Can also be prone to buildup so it’s best to avoid heavy products. Hair tends to look healthy and shiny.
High Porosity Hair:
The cuticle is wide open, allowing moisture to penetrate the cuticle, but also allowing more moisture to escape. Requires heavier products to moisturize and tends to be frizzy in humid climates. High porosity can be caused by excessive damage with chemical processes and heat exposure. Hair tends to be dry and look dull.