The hair is shaped like a cylinder. The diameter is the measurement of the horizontal cross-section of the hair strand. This measurement tells us the hair’s thickness. Hair diameter can range from 17-180 micrometers with an average diameter of 72 micrometers for women of African descent.
Hair elasticity is the measurement of how much the hair will stretch and return to it’s pre-stretched shape without breaking. When dry, hair should stretch from 5-20% and can stretch up to 60% when wet. Elasticity is rated high, normal, or low. Hair with high – normal elasticity is easily styled with wet sets and thermal styling tools. Hair with low elasticity can be more susceptible to breakage and may be hard to style.
Porosity measures how much moisture the hair can absorb and release. Porosity levels, like growth rates, are genetically determined, but can be altered due to external factors, including chemical treatments and heat styling. Low to medium porosity hair is considered healthy and can indicate that the hair has not endures damaging treatments to the hair cuticles. Excessive heat, bleaching, and dyes can transform medium porosity hair into high porosity hair. The more damage the cuticle has experienced, the hair’s porosity level increases, meaning it can absorb moisture faster. However, this also means hair will lose moisture faster. Uneven porosity can lead to uneven distribution of products.