As a relaxed head, you should know all about Porous Hair. Hair's Porosity translates to the ability of your hair to absorb moisture. Basically porosity is directly related to the health of your hair's cuticle, since the more porous the hair the more "holes" there are in the cuticle and that's not good.
If you notice that your hair is easily overly processed, dry, very fragile, and keeps on breaking no matter what you do. You likely have very porous hair. Porous hair can be caused by chemical processes (relaxers, perms, hair color), heat damage (heat tools and also SUN damage), chlorine, as well as aging.