normal porosity - this kind of hair can be thought of as being balanced. it can absorb a fraction of water, but is not overly porous. moisture can get in the hair strands and last. unlike low porosity hair, it can take chemical treatments okay, but you should keep it mind that over time the hair will become more porous by doing so.
high porosity - think of chemically processed hair that isn't being properly taken care of. this hair is damaged and has lots of holes in the hair shaft. these holes are like a sponge and absorb water easily, but this does NOT mean it's better for moisturizing. just as quick as the moisture comes the moisture goes. think of the hair strand as a house made of doors. with high porosity hair all the doors are open, making it unsafe for the cortex and insides of the cuticle. this type of hair does take in chemicals better, but it's not suggested because you'll just end up with even more damaged hair.
now that we understand the levels of porosity lets talk about the test. many of us hair fanatics know about this test. you divide your hair in four sections and take a shed strand of hair from each. this is because one section of hair might be healthier then another section. then you put the strands of hair in a tall cup or bowl and see if it floats. if it floats for a while it's healthy. here's what you should do for more clear results. see if your hair floats for at least 15 minutes. if it does then your hair is alright. if it doesn't it has high porosity and you have to up on your ph correctors. if you come back in an hour (with occasional checks in between the hour) and it's still floating, congratulations! your hair is in very good condition. now push down the strands and if they float back up (be patient!) your hair has low porosity.
here is an article that further discusses the science of hair porosity:
The "Other Path" to Moisture, by Joe Parker
here are some of the tips for low porosity hair that's explained in the article:
- If a product will hydrate your fingers then it will moisturize low porosity hair.
- Adding a tiny amount of castile soap to your deep conditioner will boost it because it will lower the overall surface energy of the water system.
- To boost your leave-in or rinsable conditioner, heat it up and apply it to your hair at an elevated temperature: 30 to 40 C.
- Hydrolyzed rice, silk and wheat proteins have a molecular weight, making them better for low porosity hair.
- 14 sodium hydroxide (lye)
- 13 bleach
- 9-11 calcium hydroxide & guanidine hydroxide (no lye)
- 9-11 permanent dye
- 8.9 castile soap
- 8-9 bentonite clay
- 8-9 ammonium thioglycolate (chemical used in perms)
- 8-9 semi permanent dye
- 8-9 baking soda
- 8 sea water
- 7 pure tap water
- 6 milk
- 5-6 tea
- 5 soft drinking water
- 5 hair
- 4-5 coffee
- 4.25-5 apple cider vinegar
- 4.5 roux porosity control
- 3-5 aloe vera juice
- 2 lemon juice