Hair Porosity: How To Measure (Sort of)

First off -  think of your hair not as a fiber like yarn because hair is more complex. Think of the inside of your hair like string cheese - protein which is flexible and retains water - it will swell when wetted. Then think of the cuticle as though you glued several layers of tiny, overlapping shingles to the outside of the cheese. You've used proteins and amino acids and lipids (fats) to glue all this together. It's flexible - but it's also prone to damage because proteins and fats do break down. Your hair's porosity is probably not the same at the roots as at the ends, the ends are usually more porous.

"Pores" are openings in the cuticle layer(s) - whether they are chipped or torn cuticle scales (imagine torn or ripped-off shingles), or cracked, shrunken and fused, or simply not glued down very well. Any of these situations leads to a less-protected hair cortex - which means your interior of string cheese will dry out more quickly.©Science-y Hair Blog 2013

Why the Float Test Is Inaccurate:©Science-y Hair Blog 2013

The "float test" for hair porosity is one in which you try to float a strand of hair in water. It is supposed that a porous hair will immediately begin to absorb water, become heavy, and sink. But there are some flaws in the design. See this post for an update to the float test.

•  First of all is surface tension of water. The molecules at the surface of water stick together where air meets water. Like a "skin" on the water. If you place a light-weight object on the surface of the water gently, it will float. You can make sewing thread and even dry sand float on water this way. So let's say you have a very lightweight, but porous hair and you drop it in a glass of water. The surface tension may well override the weight and porosity of the hair strand and it floats - even after many minutes have passed.
• Second - specific gravity. Hair and water have a similar specific gravity. Things of similar (or lesser) specific gravity to a given liquid will float in that liquid. Dry hair is buoyant in water - like ice or driftwood.
• Third: What is on the hair? Is the hair heavier due to the weight of a product? Is that product repelling water? Is that product a wetting agent (like hair conditioner) which will cause the hair to become wet more quickly and sink?

Arrows show where the cuticle has chipped away due to sun

and friction.

See what I'm getting at? Too many variables. And for porosity, your own observation is going to take many variables into account which will give you plenty of relevant information.

One of the most accurate ways of measuring hair porosity is using gas sorption to determine total pore volume (holes in the surface) - which is expensive and absolutely not do-it-yourself. It measures how much of a given gas can be taken into hair - hair which has more pores will take on more gases. Hair can also be examined under a microscope to determine how much chipping, wearing away, or lifting there is in the cuticle. This is purely visual. Weight of water taken on by a dehydrated hair sample could be measured, if you had a bunch of other samples to compare to for reference material. All impractical!©Science-y Hair Blog 2013

Most very accurate methods of measuring porosity are not accessible to most people and that's okay because it is really easy to determine. This post has more information about hair porosity, some of which is about to be repeated.

Porosity matters because it determines how much protection your hair needs (what you'll apply to it) and how quickly it will lose water. It also determines how well or quickly your hair takes color. Porous hair loses water more quickly than hair which is not especially porous. Dehydrated hair (like dehydrated string cheese) is less pliable, breaks more easily, has less shine and does not hold a shape (like a curl or wave) neatly.

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. Learn by studying!? Yes, this is sensory and multi-faceted. You are the best judge of your hair's porosity - here are some hints.©Science-y Hair Blog 2013

This hair is fairly healthy - the cuticles are intact
and fit tightly over one another - not very porous.

Not-porous hair: Your hair is not porous if it is very shiny. Try folding a wide strand of clean hair (no styling products) over a finger - does it shine brightly? If you do not heat-dry your hair with high heat or use curling or straightening irons, do not spend much time in the full sun, do not brush your hair often or do not color or bleach (highlight) it - it's probably not very porous. If your hair does not absorb oils and conditioner and becomes greasy or limp easily, it's probably not very porous. Not-porous hair takes permanent waves (perms) poorly and resists chemical straightening and hair dye. Not-porous hair does not tolerate lots of conditioner or oil - it will become oily-looking and limp (although this variable overlaps with the diameter of your individual hairs quite a lot). Not-porous hair will not dramatically change with more conditioner or deep conditioners because it is not losing a lot of water under most conditions - its cuticle fits snugly and there are not a lot of cracks and chips. Products (hair conditioners, oils, styling products) do not seem to "soak in" to not-porous hair. Not-porous hair is easy to maintain in a healthy condition. There is no reason to try to make it act more porous so that you can apply products to make it softer. Hair products like conditioner are actually designed to make hair behave as though it is not-porous. So if this describes your hair - life is good!©Science-y Hair Blog 2013

This hair is showing normal porosity - the cuticle looks

like shingles on a house - you can see this at the edge of the 

hair.

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.©Science-y Hair Blog 2013

A kink in a hair where it is both narrowing and twisting.

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. It may lose dyed hair color rapidly because of the porosity.

• Kinking and porosity: Kinking in hair creates an uneven surface and it may be difficult for cuticles to lie flat and smooth when the hair shaft they're attached to is widening and narrowing or torque-ing (twisting). Any uneven surface accumulates more friction than a smooth surface. If a cuticle sticks out a bit, it is likely to be chipped or broken off. Kinking hair can be more vulnerable to increased porosity when exposed to daily wear and tear because it suffers more friction from everyday living than non-kinking hair. This photo (above, right) shows a porous hair with kinking (a kinky, curly hair). Kinking can occur in any hair - straight, wavy, or curly. Not every person with kinking hair will have porous hair - and you can look at people in your family to see whether you inherited hair that tends to be extra-thirsty or not. There are many variables involved, but this is an important one to know about because people with kinking hair usually need plenty of "slip" in conditioners to reduce friction. I'm fascinated by the patterns and frequencies of kinking in hair, so I digress...

Arrows show "lifted" cuticle which is one type of pore,

making this hair moderately porous. This is a little tricky to 
photograph. Lower down there is an indentation which
is where a piece of cuticle has broken off.

• Environmentally porous hair (damaged hair): Hair becomes porous with high-heat styling tools (curling/straightening irons, hot rollers, blow dryers on high heat without diffusers). Hair becomes porous with a lot of sun exposure or a lot of swimming in chlorinated water or salt water. Bleaching or highlighting immediately make hair more porous - up to 30% more pores than prior to bleaching - this is similar to the increase in porosity from 200+ hours of direct sunlight exposure. Brushing hair a lot, shampooing frequently, regularly wearing barrettes or tight clips, ponytail holders all can shear away pieces of cuticle or entire scales, leaving gaps. Friction of a handbag over hair, hair tucked into a collar, under a hat and so on also shear off cuticles. 

This hair has substantial sunlight, chlorine and friction 

damage. Notice you can barely see any cuticles. This

is not bad focus in the photograph, it is hair damage. This hair

is quite porous.

Porous hair usually takes on dye, permanent waves and chemical straightening quickly. And loses dye quickly. Porous hair loses moisture easily. The hair in this photo is porous because of all the sunlight and brushing and chlorine it was exposed to over many years. In this case, most of the cuticle has been sheared off and is not visible. It has a difficult time retaining moisture.©Science-y Hair Blog 2013

References:

Hessefort, YZ, Holland BT, Cloud RW, 2007. True Porosity Measurement of Hair: A New Way to Study Hair Damage Mechanisms. Journal of Cosmetic Science

Chemical and Physical Behavior of Human Hair 

Robbins, 1994. 3^rd Ed. Springer-Verlag, New York

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