What characteristic does porous hair have that affects its interaction with chemical solutions?

Porous hair exhibits a raised cuticle layer, which significantly influences how it interacts with chemical solutions. The raised cuticle layer allows for greater absorption of these solutions because the open spaces between the cuticle scales facilitate the entry of chemicals into the hair strand. This characteristic is particularly noticeable when applying hair color or other treatments, as porous hair can absorb the product more easily and may process differently than hair with a flat or tightly layered cuticle.

In contrast, options related to flat cuticle layers, thick cortex, or thin medulla do not convey the same impact on chemical interaction. A flat cuticle layer would typically create a smoother surface, reducing absorption, while the thickness of the cortex mainly affects the hair's overall strength rather than its chemical properties. The medulla, being the innermost layer of the hair, has minimal influence on how hair interacts with chemical solutions. Thus, the presence of a raised cuticle layer is key in determining the hair's porosity and its subsequent behavior with various treatments.