How porous or absorbent your hair is has a lot to do with how it looks and can help you decide what to use on your hair to help it look it’s best. A porosity is a hole or a gap – an opening.
Hair which is porous [aka high porosity] will take on water and other chemicals easily because of all the tiny openings in the cuticle. Water gets in and out easily.
Hair which is not very porous [aka low porosity] repels water and most other fluids and this is a good thing. Water doesn’t get in or out easily.
It’s fairly common to have hair that is porous on the ends, but not at the roots.
What causes porosity?
Weathering of hair, mechanical stress [combing, especially brushing, tieing up, rubbing, etc.], wetting and drying, shampooing, chemical treatments, and physical structure of hair. If your hair has waves, curls or (especially) kinks (and wavy hair can be kinky hair too), it is likely to have areas on the strand which are narrow, flattened, twisted or otherwise not as strong. Even the “cuticle armor” cannot protect these areas adequately. These are prone to breakage and damage and therefore become porous easily. Wavy and curly hair is also more prone to damage from daily life simply because it has bends in it.
How to Determine Your Hair’s Porosity:
This is something you learn from studying your hair by running your fingers over a hair strand, observing shine or reflectivity, how hydrated your hair feels on a daily basis, and your hair’s response to products.
Normal-porous hair: It shines, maybe not quite as much as not-porous hair. It perms and takes color as expected. Your hair can be normal-porous even if you use some heat on your hair (low-heat diffusers). Normal-porous hair does not become oily-looking with reasonable amounts of conditioners or oils. Normal-porous hair may have times when it feels a bit dry, or not dry at all and it is easy to make it feel “not dry” and soft with hair conditioner and gentle care. You perceive some “soaking in” of hair products. You probably have had some exposure to the full sun, possibly chlorinated swimming pools. Your hair may be not-porous near the roots and normal-porous further down and therefore respond differently to conditioners in those two areas, which is why many people condition their hair from the ears, down. If you run your fingers up and down an individual hair, it feels mostly smooth. This normal-porous hair has cuticle scales which look like shingles on a roof. They overlap and don’t stick up much.
Porous hair: If you run your fingers up and down a hair strand, it may feel bumpy and uneven due to kinking, or to damage. Quite porous hair does not shine much and though it may have some gloss, it’s not “reflective” or brightly shiny. It will seem to absorb hair products of any kind, tends to feel dry most of the time and you have a difficult time getting it to feel soft and pliable. Porous hair usually takes on dye, permanent waves and chemical straightening quickly. And loses dye quickly. Porous hair loses moisture easily.
Maintain Porosity:
Avoid too much handling, tight ponytail holders, excess heat (curling or straightening irons, blowdryers without a diffuser), prolonged exposure to sunlight, chemical treatments (permanent waves or chemical relaxers), and bleaching or permanent haircoloring. Don’t rub your hair roughly with towels, tie it up tightly every day, use metal barrettes with sharp edges. Avoid brushing or combing vigorously and with force. Do detangle with care, don’t wash hair every day, use dilute shampoos or mild shampoos.
Taken from:
https://science-yhairblog.blogspot.com/2011/09/porosity-in-hair.html
https://science-yhairblog.blogspot.com/2012/06/hair-porosity-how-to-measure-sort-of.html
I always called my hair “resistant”, before low porosity was a common term, and I think that’s a reasonable way to think about it. It takes a little while to get thoroughly wet, resists chemical treatment (when I used to do that- though obviously once chemically treated it lost that quality. That was the biggest clue. To bleach my own hair took about 6 hours of processing to bleach, 4-5 rounds over 2 days. My kids with same color hair take 1 or 2 rounds of bleach, less than an hour of processing. My brother in law, 15 minutes of processing got him to the same color mine took 6 hours to achieve, though his hair looked just like mine!). Resists damage, too. So when I grew it super long, no split ends.
But also resists conditioner, tends to get dry & stiff, wiry. Needs leave in to add pliability.
Strongly agree that the tighter the curl, the more likely hair is to be porous, just because making those tight curves can lift the cuticle. And I think fine hair also more likely to be porous (or to act porous), as there is just less hair in each hair.
Your hair is very healthy then, whatever you’re doing is working! I’ve heard adding heat from a cap can help penetrate low porosity hair. I bought one earlier in my journey before I realized I didn’t need it. It’s just a cap with some flaxseeds in it that I would put in for less than 1 minute in the microwave.
My hair is pretty fine, even with gentle care it is still high porosity. Fine hair lacks a medulla and gets beat up easily lol. There’s this textbook about hair a lot of people reference and it describes porosity as how damaged hair is. Also hair stylists use a 5 grade system to measure porosity. I wasn’t sure if I should go more into it about this since the post is already long. Maybe a part 2 is something I can work on in the future. I think I read somewhere that people think very curly hair is coarse but usually it is fine because of all the kinks, there’s just a lot of it.
Yeah people use “coarse” to mean not smooth, or unmanageable. Technically it’s exactly what you say though - wide gauge hairs. If I laid one of my hairs next to one of each of my children’s hairs, mine would be like if you twisted all of theirs together into a yarn! My hair is thick, but only because each individual hair is thick, it’s not particularly high density. One of my kids has the same size ponytail and fine hairs, I think they probably have 10x as many individual hairs as I do.