Porosity is your hair’s ability to absorb and retain moisture. It is affected by the flexible outer hair layer called the cuticle, which determines how easily moisture and oils pass in and out of your hair. For most, porosity is genetic, but it can also be affected by external factors such as exposure, environmental radicals, hair manipulation (certain protective styles) heat treatments and chemical processing. Knowing your hair's porosity can help you choose the right sequence in which you use your products to keep your hair well-moisturized, juicy, strong, and shiny.