Hair porosity is defined as the ability of hair to:

Hair porosity refers to the hair's ability to absorb moisture, which is a critical factor in hair care and styling. Hair porosity is determined by the condition of the cuticle, the outermost layer of the hair strand. When hair cuticles are tightly packed, the hair has low porosity, meaning it resists moisture absorption. Conversely, when cuticles are raised or damaged, the hair has high porosity, allowing for easier moisture penetration but also making it more vulnerable to damage.

Understanding hair porosity is vital for selecting suitable hair care products and treatments. For example, someone with high porosity hair might benefit from heavier, moisturizing products that help seal in moisture, while someone with low porosity hair might need lighter products to avoid buildup and ensure effective absorption.

Other considerations like hair styling and growth are important but do not directly correlate with the definition of porosity. Thus, the correct answer emphasizes moisture absorption as the fundamental characteristic of hair porosity.