I have often said that I do believe that these type of tests are really very poor and very unscientific. Let me explain why:
1. Hair in general will almost always float in water.
Many of you doing this test will note that your hair will float for ages and it may take some prodding to make it sink if it does at all. This is because hair is generally covered in oil. This oil is naturally produced sebum and any extra that you may use in your hair care routine will have an added impact. Now oil will always float on water, so your hair floating does not mean that it has low porosity. It does mean that your hair is light (which it is) and has a coating of oil that repels water (which it does).
2. What would happen if you washed off the oil on hair using shampoo then performed the test?
If you chose to do the test with hair that is freshly washed but not conditioned then that is really an artificial test because you would normally apply conditioner after a shampoo (Of course if you only shampoo then this test is not artificial for you). For most people hair will still float because there is usually still some residual oil.
3. Warm water or cold water?
Some say the temperature of the water does not matter but on a scientific level this is probably not true. The reason for this is
- Hair has a thin oil coating (warm/hot water removes oil to some extent)
- Hair is protein (most proteins will have small changes in structure if temperature changes)
However, the most likely observation that most people will have with a single strand of hair is that it will float.
4. If hair sinks, is this because it has taken up water?
If you place hair strands in water they are going to take up water, this is a fact and this is normal. The more your hair takes up water, the heavier it will get but it may still float because of the oil coating. Hair could indeed sink and many relate this to damage (bleaching or relaxing hair for example makes the cuticle more porous) but it could also be that your hair is naturally dense (i.e naturally weighs more).
So is there a scientific test to know how porous hair is?
Yes, there is and much like the proven tests to see if oil penetrates hair, it is a lab based test that is generally not an easy or cheap method to do. It is called gas sorption and involves detecting the flow of a gas (or air) through hair. It has been used to show that bleaching and UV damage do both indeed greatly change the porosity of hair ( Journal of cosmetic science 59.4 (2008): 303)
Is there a home - test for porosity?
There is no single test that I would say is reliable. Many people think that hair repelling water is a bad thing but it really is not, it is excellent. It means your hair has its oil coating and is working well. The oil coating cannot fully block out water coming in or out, it is a permeable barrier.
I do absolutely advocate for people to reject or accept products based on how they work. If a product leads your hair to be constantly dry, leave it. If a product makes your hair too mushy, stop using it. Find products that work by trusting yourself and your hair.
Are you doing the sink/float porosity test? Did you find that you were low or high porosity? How did it help you? After reading this article would you reconsider?