Good question. I was not quite sure, so I went back to some of the literature here. I pasted GymFreak's quick description of porosity and I think it answers your question...or at least I hope it does. Here it is, I underlined the portion that should address your question:
Porosity
If you are constantly dealing with dryness, you might want to also look into checking your hair’s porosity.
What is your porosity and why should I care?
Porosity is your hair’s ability to absorb materials like water into the hair. Think about it like a sponge. First of all imagine a brand new sponge. It will have tiny holes in it, and when you immerse it in water, it will soak up a large quantity, and be able to hold that liquid for a long period of time. This is because it has good porosity.
Now imagine an old sponge. Its holes have become damaged and distorted. It might even be torn in some areas. When you immerse this sponge in the same amount of liquid, it will absorb far less and will certainly not be able to retain the moisture so readily. You should care about your porosity because Hair that has poor porosity will not be able to absorb or retain moisture as well as hair that has good porosity, making hair permanently dry. Poor porosity can and will cause breakage issues too.
How to test your porosity
One way- Test the porosity of your hair. In order to test accurately for porosity, use three different areas: front hairline, in front of ears, and near the crown. Grasp small strands of dry hair and comb smoothly. Hold the ends firmly with the thumb and index finger of one hand and slide the fingers of the other hand from the ends towards the scalp. If the fingers do not slide easily, or if the hair ruffles up as your fingers slide down the stand, the hair is porous.
The more ruffles formed, the more porous is the hair. The less ruffles formed, the less porous is the hair. If the fingers slide easily and no ruffles are formed, the cuticle layer lays close to the hair shaft. This type of hair is least porous, is most resistant and will require a longer processing time.
How do I fix it
In order to help correct porosity issues, you need to focus on keeping your hair cuticles as smooth and flat as possible. Clear rinses, protein treatments and watching the pH of your products will all help with your porosity.
For more detailed info check out these links
http://www.longhaircareforum.com/for...light=porosity
http://www.associatedcontent.com/art...y_damaged.html
http://www.associatedcontent.com/art...y_damaged.html