Wet hair dries from the place where it is most porous. Porous refers to spaces or holes in the hair where product, air, or water seeps out or comes into the hair. I classify hair as either high porosity or low porosity, meaning the percentage of porousness discovered. If hair takes a significant amount of time to dry that means there are zero or few holes in the hair strand, this is low porosity. High porosity is the exact opposite in hair, it dries quickly. Highly porous hair struggles to retain moisture.