Hair Porosity

Hair porosity is a measure of the hair shaft's capacity to absorb water and water-soluble products, and its ability to retain that moisture once absorbed. It is determined by the condition and configuration of the cuticle — the overlapping, scale-like outer layer of the hair shaft. When cuticle scales lie flat and tightly overlapping, the hair shaft is less permeable to water and is classified as low porosity. When cuticle scales are raised, lifted at the edges, or widely spaced due to damage or natural geometry, the shaft absorbs moisture readily but loses it just as easily, and is classified as high porosity. A third classification — normal or medium porosity — describes a cuticle that absorbs and retains moisture at a balanced rate without the extremes of either end. Porosity is influenced by genetic cuticle geometry, the degree of chemical processing the hair has undergone, cumulative heat damage, and the natural weathering that occurs over the lifespan of a hair strand from root to tip.

Porosity is the most important single variable in determining which products will work for a given head of hair and how they should be applied. Identical products applied to low and high porosity hair will produce dramatically different results because of the difference in cuticle permeability. Low porosity hair requires heat during deep conditioning to open the cuticle, lightweight water-soluble products that can enter the shaft, and the avoidance of heavy oils and butters that sit on the surface and create buildup. High porosity hair requires protein treatments to temporarily fill cuticle gaps, heavier creams and butters to seal moisture in after application, and cool-water rinses to encourage cuticle closure. Without knowing your porosity, product selection is guesswork. With it, every decision has a rationale.