Porosity is a term used in hair care to describe the hair's ability to absorb and retain moisture. A good analogy would be to consider your hair like a sponge. When the sponge is new it is very porous and absorbs water thus it has good porosity. On the other hand an old sponge where the tiny holes have been damaged does not absorb water as well as it used to.
The hair shaft is made up of cuticle layers which are actually overlapping scales. When the cuticle layer of the hair is tightly woven and compact it has low porosity as it inhibits moisture going in and going out. Low porosity hair is resistant to hair coloring and perms and must be softened to open the cuticle layers prior to a treatment. The best remedies for low porosity hair are deep conditioning products and products rich in moisture and/or products that contain humectants which will attract moisture to the hair.
High porosity hair on the other hand has an open cuticle layers and absorbs moisture and color treatments more easily. However overly porous hair releases moisture and becomes dry and dull. The best products for hair with a high porosity are moisturizes containing natural plant based oils, and mildly acidic rinse. Additionally one should avoid sulfate-based surfactants.
Normal hair porosity is somewhere in the middle. This hair texture requires the least amount of maintenance, as it will allow moisture to pass in the hair shaft as needed. Additionally hair with a high porosity will hold a hairstyle and allow chemical processes in the expected manner. However, note that repeated chemical processes can change the porosity of your hair by damaging the cuticle layer.
So how do you test hair porosity? Below are a few tests you can do to figure out your hair's porosity.
Wash and condition your hair as normal.
Towel dry (do not add any other products)
Gather one strand of hair and run your index finger and thumb along the shaft starting from the end of the hair strand to the root.
Low porosity will feel slick
Normal porosity will feel smooth
High porosity you will feel catches as you move your fingers down the hair shaft.
Take a few strands of hair (from comb or hair brush) and place in a bowl of water. If the hair sinks to the bottom of the bowl in less than a minute or two, it is porous. If only a part of the strand sinks you your hair is porous in certain areas and this is quite common.
When washing your hair notice how long it takes for your hair to become saturated and fully wet. Hair that wets easily is porous, much like a new sponge. There is also a possibility that you hair could be covered with to many hair care products such as oils and conditioners. Additionally consider how long it takes your hair to dry, hair that dries quickly is porous as the cuticle layers are open and allow air flow.
I hoped this article helped you to understand hair porosity and bring you that much closer to selecting the right hair products for your hair.