Hydrating Low Porosity Hair: It’s all About the Energy Baby!-Technically Speaking

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In the last article, “How to Hydrate Dry Hair Caused By High Porosity, we discussed how to moisturize high porosity hair.   The discussion was basically about the mass transfer of hydration.  Some people were saying that oil is a moisturizer and I countered with oil doesn’t have one drop of water so how can it be a moisturizer?  What really bothered me about the oil and moisture statement was that it did not respect one of the most fundamental laws of nature (Conservation of Mass).  Conservation of Mass states that mass can neither be created nor destroyed, only transformed.  Since adding oil to hair does not involve a reaction, water can’t be created.   I went on to say that we have to add water to our hair in order for an oil to appear to be moisturizing.  Hopefully, after reading the high porosity article, you all are on your way to having healthy, moisturized hair.  But what should you do to achieve moisture if you have low porosity hair?


In this article, I want to discuss hydration of hair from the perspective of the second most important law of nature.  It is the Conservation of Energy.  Just like mass, energy can’t be created or destroyed, only transformed.  We don’t realize it but mass at its most basic level is energy and energy is mass. They are in equilibrium with each other. So without getting too Zen, a particle’s mass, energy and momentum all co- exist simultaneously and are in equilibrium,  yet they only have relevance in the present moment.

So, in this article I want to have a conversation about the energy of hydration for the special case of low porosity hair.


It All Begins With the Cup Test for Determining Hair Porosity!

Most people are aware of the cup test to determine one’s porosity.  For those who don’t know, the test goes as follows:

You take a strand of freshly shampooed hair and place it in a cup of water.  If it floats on the top of the water after several minutes, the hair is said to have low porosity.

However, I purposely left out one important piece of information-The water is at room temperature.  What do you think would happen if I used hot water instead of room temperature water?  The same strand of low porosity hair will eventually sink from the surface of the cup.


Exactly How does Temperature Affect the Wetting of Low Porosity Hair?

The increased temperature of the water is the result of my intentional addition of energy.  It does not matter how I heat the water system.  For example, let’s assume I used a microwave oven.  At the start, water molecules, which are at room temperature, are in equilibrium with each other.   Once the oven is turned on, the water molecules absorb the microwave radiation and the electrons begin to vibrate and expand.  What is really happening is the microwave radiation (radiation energy) is converted into kinetic energy (due to vibrating electrons).  Kinetic energy is converted to thermal energy as a result of the friction created when electrons are rubbing together.  The thermal energy increases the water temperature, which in turn is absorbed by the hair system.  Under increased temperature conditions, the hair cuticle begins to open and the water penetrates the hair shaft.  The same argument can be made if you use an electric stove or gas stove to heat the water.  In these cases you are using electrical energy and converting it to thermal energy or combustion energy, which converts to thermal energy.


  • Tip for moisturizing low porosity hair:  In the words of my 10 yr. old daughter, “Heat is your BFF!’  Heat makes it possible for you to open those cuticles and allow water to penetrate the cell membrane complex (CMC) and cortex.   The absolute best way to heat the hair and add moisture is with a steamer and pre poo or deep condish regimen.  Most people do not realize it but when steam condenses it will give up 1000 BTU/lb.  That’s a huge amount of energy to rapidly change the hair temperature (cuticles) and moisturize all at the same time.  At atmospheric conditions, steam will condense once the temperature is below 212F.  The air and your hair act as a heat sink to absorb this energy.  Hair dryers take longer and do not bring additional moisture.


But wait-I’m not done yet!   There is something else going on with the water when I raise the temperature.  It has to do with something called surface tension. What is surface tension and why is it important for hydrating hair?


The Basics of Surface Tension

Surface tension is the property of a liquid that allows its surface to resist an external force.   The ability of a liquid’s surface to resist an external force is directly related to it cohesive force.      Cohesive forces are inter-molecular forces that hold a liquid together.  These inter-molecular forces are attractive forces of like molecules.  Depending on how strong these forces are, liquids will form droplets or fine mist.    By convention, the units of surface tension are force per unit of length.  You can think of it as how much force is needed to be applied in order to submerge a fiber a certain distance into the liquid.

Solids have cohesive forces also.  For solids, by convention we use the term surface energy, which has the units of energy per area.  Think of it as how much energy is needed to be applied in order to wet the surface area of a solid.   Don’t get hung up on the units because they are interchangeable.  I can use surface tension to calculate surface energy and vise versa.


Let’s go back to the porosity test and explore how surface energy is relevant to hair care!

So now that you know about surface tension, what is really happening with low porosity hair?


In the hair care business, we define “the floating of low porosity hair on the surface of water” as low porosity hair’s inability to be wetted by water.  You have a surface energy imbalance.  The surface tension of the water is greater than the minimum required surface energy of the hair fiber.  Here is another way to look at-In order to wet a hair fiber the surface energy of the water has to be approx equal to or less than the surface energy of the hair fiber.

Wet ability = Spread Factor = Surface Energy Dry Hair – Surface Energy Water

If wet ability is negative, then the hair fiber becomes only partially wetted. Depending on how negative the wet ability is determines how wet a fiber will get.

If wet ability is zero to positive, then the hair will be totally wetted.

Let’s take a look at some real numbers.


Surface Energy  
Virgin Hair


Damaged Hair


Water @ 20C


Water @ 100 C


Steam @ 150 C






Stainless Steel



Let’s assume virgin hair is an approximation for low porosity hair.  As you can see, the surface energy of water at room temperature is almost 3 times as large as the surface energy of the virgin hair.  Based on the equation for wet ability, we now see why low porosity hair is difficult to wet (0.028-0.73 =  -0.045) . We also see how increasing water temperature or using steam brings you much closer to achieving total wetting of the hair fiber (0.028 – 0.059 = -0.031).  From an energy perspective, you can now see how using thermal energy lowers the surface energy of water to bring about more favorable results as it is related to the hydration of low porosity hair.

Let’s look at what the wet ability will be for high porosity/ damaged hair.

0.042- 0.073 = -0.031

So at a surface energy of -0.031 N/m, the hair will be partially wetted.  It is important to note that you do not have to achieve total wetting (wet ability = 0) in order to hydrate your hair.  Great if it can be achieved but not needed to hydrate the hair.  The goal is to get at or below

-0.031 N/m.


Note:  Increased water temperature helps high porosity hair as well!


The Experiment

Use a dropper and add one drop of water to a stainless steel pot and to Teflon coated pot.  The Teflon coated pot will have a water bead while the stainless steel water droplet will be slightly raised at best.  This is exactly what happens when you place low porosity hair in water at room temperature.  The low porosity hair is like Teflon and water.  The energy imbalance is too high and water will bead up.  On stainless steel, the energy balance is less pronounced so the surface can be wetted.

Another way to reduce the surface tension of water is to add a surfactant.




Surface Energy  
Virgin Hair


Surfactant @ 0% (Pure H20)


Surfactant @ .003%


Surfactant @ .004%


Surfactant @ .005%



Based on the data, small amounts of surfactant can have a huge effect in lowering the overall surface energy of water.  With as little as 0.005% of surfactant added to water the surface energy requirements can be lowered to the point were it is almost equal to the virgin hair.

Surface Energy of Virgin Hair: 0.028

Surface Energy of Water with 0.005% of surfactant: 0.03

Very low differential of energy, thus the hair fiber is easily wetted.


  • Tip:  Adding small amounts of surfactant to your deep conditioner will lower the overall surface energy of the system and drive hydration.
  • Super Tip:  Adding a tiny amount of Castile soap to your deep condish regimen will drive hydration for several reasons.  The first is that it will lower the overall surface energy of the water system.  The second is that the castile soap tends to have a higher pH and it will also open the hair cuticle (more on this later).



Conditioning the hair is the process of smoothing down the hair cuticles aka detangling.  From an energy perspective, you are reducing the surface energy of the hair slightly less than 0.028 N/m.  The smoother the surface, the lower the surface energy and the more difficult it is to hydrate/ wet the hair.  Smooth surfaces have lower surface energy.

The same principal can explain why high porosity hair is easily wetted.  The surface energy is increased and is closer to the surface energy of water at room temperature.  Net-Net, when hair is at the elevated surface energy you are more likely to wet the hair.


However, this is only half the story for conditioners.  The actual conditioner solution has a significantly lower surface energy as compared to water.  This is due to the presence of a special class of surfactants called emulsifying agents.  This is why some leave in conditioners will foam slightly.  They can decrease the surface energy of the conditioner and range in value from 0.063 to 0.03 N/m.

The diversity of surface energies in products is one of the reasons why some products will perform on one person’s hair and will not perform on another person’s hair.  We tend to say, the product is bad.  In reality it’s not bad or good.  A better way to think of it is the surface energy of the product relative to the surface energy of your hair is such that you can’t achieve satisfactory wetting.  Or, put another way, we do not have enough energy in the system to achieve wetting.

  • Tip:  A good rule of thumb is that if a product will hydrate your hands, in particular your fingers then it might also be good on your low porosity hair.  The skin around the fingers has a surface energy of 0.026 – 0.029 N/m.  This is very close to the surface energy of low porosity hair.

If you have damaged or high porosity hair, then a topical application of the condition to your forearm is a good test to see if it will moisture your hair.  The surface energy of the forearm is 0.038 N/m

  • Tip:  If you want to increase the performance of your leave in or rinsable conditioner, try heating it up and applying it to your hair at an elevated temperature.  Get a baby bottle warmer and empty plastic bottle.  Add the conditioner to the plastic bottle and heat it up to 30 C to 40 C.


Stop!  I want to make sure that everyone is clear that I am not proposing that you boil the conditioner.  If you heat the product too much you can break the emulsion and burn yourself.  So stay below 40 C or so.

By now, you can probably tell me the effect on surface energy.  At elevated temperatures, the surface energy of the conditioner is decreased.  Also, the porosity is increased due to the cuticle opening at higher temperatures.  The end result is that you hair is more likely to be wetted.


Hydrolyzed Proteins

The type, size and molecular weight distribution of hydrolyzed proteins is especially important for the hydration of low porosity hair.  Due to the nature of the cuticle spacing, the smaller hydrolyzed proteins are better at filling/repairing the damaged hair fiber.  From an energy perspective, adding hydrolyzed protein is similar to adding conditioning agents.  The hair surface energy is reduced because the protein fills the cracks in the hair fiber (smoother surface).  Remember, smooth hair surfaces are more difficult to wet.   However, this is just like the conditioner example.   The protein conditioner solution’s surface energy is vastly lower than water @ room temperature.  So net net, they can do a better job hydrating the hair.

  • Tip:  Look for hydrolyzed rice, silk or a wheat protein.  They tend to have a molecular weight profile that is really good for penetrating and coating low porosity hair.

Look out for oat, animal keratin or corn-hydrolyzed proteins.  They tend to be too large for use on low porosity hair.



The intentional addition of high pH  (base) or low pH (acid) to your hair products will also change the energy balance of the hair system.  In low pH conditions, the hair cuticle will open and the hydration of low porosity hair can be increased.  Rough hair surfaces are easier to wet.

Two things are happening when we change the pH of hair products by adding a base.

The first is that we are increasing the energy of the water system by the heat of hydrolysis.    When a base is added to water, heat is generated.  A good example of this is when you make soap.  When caustic is added to water, heat is generated and the surface energy for the water is decreased.

The second is that the increased heat and high pH also reduces the surface energy of the hair as the cuticles open as a result of breaking the hydrogen bonding in hair (reversible process).

  • Tip:  As stated earlier adding castile soap is a good way for low porosity hair to get extra moisture and hydration.  I am not saying that this should be done every time you deep condition your hair.   Just try it on some frequency and test the results.  Also, you do not have to use a lot of surfactant either.  Just a little surfactant is needed to reduce the surface energy of the conditioner product.

I had read where folks were using sodium bicarbonate to change the pH of conditioners.  I am not a big fan of this approach because sodium bicarbonate is not completely water-soluble.  Here is some solubility data for Na Bicarb.

Stop!  I want to be very clear that I am not saying that using Bicarb is wrong.  What I am saying is that in my opinion, castile soap is a better way to change pH.

Solubility of Na Bicarbonate at various temperatures

69 g/l (at 0ºC)

96 g/l (at 20ºC)

165 g/l (at 60ºC)

What the data is saying is that I can only add 69 g of Na Bicarb per 1 liter of water @ 0 C.  If I go over that amount, the solids will precipitate out of solution.  The solution goes from clear to cloudy.   Using Bicarb takes a little more work to rinse out un-solubilized Na Bicarb.  If I were going to use it, I would rinse with Green Tea, Lemon Juice or Apple Cider Vinegar to neutralize it.

Also the solubility of Na Bicarb increases with higher water temperatures.  So using high temp water helps.  Since you are now experts on surface tension, you know why rising the temperature will help drive the solubility of Na Bicarb.  This is a blessing and a curse, you have to maintain the temperature or Bicarb will precipitate out of solution as the temperature cools.

Here are my thoughts on why castile soap might be a better choice than Sodium Bicarbonate for increasing the pH of your conditioner.


Na Bicarbonate


  1. Drives hydration
  2.  Works with condish and emollience is not compromised


  1. Not completely water soluble and must be completely rinsed from hair (gritty/abrasive)
  2. Extra Neutralization Step needed with weak acid (lemon juice, green tea or ACV)
  3. Mildly damaging to hair (will lift the cuticle)


Castile Soap


  1. Drives hydration
  2.  Completely water soluble


  1. Can compromise the emolience and conditioning performance if too much is added
  2. Mildly damaging to hair (will lift the cuticle)


Summary for low porosity hair care.

  1. Give yourself more time to allow hydration to occur.  Low porosity hair takes longer to hydrate.
  2. Look for ways to add heat to your condish products.  Steam is the best, but low heat dryers are good too.  The goal is to get heat and product into your hair.  Consider heating the product, if you are averse to using a hair dryer.   
  3. Consider using a tiny bit of surfactant in your next deep conditioner or co wash.  I like castile soap but other no poo shampoos might be equally helpful.  Check the pH. The pH should be 9 for castile soap.
  4.  If you are using protein conditioners, look for hydrolyzed rice, silk or wheat.  Beware of corn and oat protein because they are too large. 
  5. Occasionally use castile soap, such as the CUSH Mango Babassu Shampoo Bar to shampoo your hair.  The elevated pH will drive hydration.  I am not saying switch to castile soap for all your shampooing.  Just work it in once every 3 to 6 weeks.



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