Porosity is basically your hair's ability to hold moisture. Some people's hair seem to always be soft, shiny and moisturized while others not so much. You can beat this trick your hair plays on you just by knowing. This is determined by the way that the cuticle(outer most layer) lays.
Low Porosity (Compact):
-Your hair tends to have a hard time absorbing moisture, but has no problem holding on to it.If you are washing your hair in the shower, at the first sight of water, the water just seems to bounce off and not really absorb right away. You only need to moisturize your hair everyday to every couple of days.(The cuticle is more restricted)
-Your hair tends to absorb moisture easily and has a hard time holding on to it.Your hair needs to be moisturized many times a day. (The cuticle is raised)
I definitely have low porosity hair. When it rains and I'm outside, my hair hardly ever gets "wet." The water just bounces off. Want to know your level?
Find a piece of shed hair in your daily styling tools. Shed hair is hair that has a small white ball on the tip. If you do not see the white tip, it is a broken hair and cannot be used for this test. Once a hair is found, drop the hair into a glass of water. If the hair sinks quickly, it has high porosity because it adsorbed the water quickly. If the hair floats at the top for a while it has low porosity because it has trouble absorbing the water. If the hair slowly sinks, the porosity is normal.