Reviewed November 8, 2026
Hair Porosity: The Float Test, and What It Gets Wrong
Porosity is how easily your hair absorbs and loses water, and it decides which products work. The float test, dropping a strand in water and watching it sink or float, is unreliable because surface oils and product buildup change the result. The strand slide test is better, and it takes ten seconds.
Porosity is the word hair care uses for a simple question: how easily does your hair take in water, and how fast does it lose it. Low porosity hair resists water and resists product. High porosity hair drinks water fast and dries fast, and it loses moisture just as quickly. The products that work for one fail on the other, which is why knowing your porosity matters more than knowing your curl pattern.
The float test is how most people try to find out, and it is the worst of the common tests. A clean strand floats differently from a strand with conditioner on it, and a strand with oil on it floats differently again. The test measures what is on the hair, not the hair itself.
Why the float test fails
The test says to drop a clean strand in a glass of water and wait: floating means low porosity, sinking means high porosity, hovering in the middle means medium. The problem is that a strand is never clean in the way the test assumes. Sebum, conditioner, styling product, and hard water minerals all coat the cuticle, and the coating decides whether the strand floats, not the porosity underneath.
The second problem is time. A low porosity strand will eventually sink if you leave it long enough, because water gets in slowly, not never. A test with no time limit has no answer, and the versions online disagree on whether to wait two minutes or four. A test that cannot agree with itself is not a test.
The strand slide test
Take a single strand, hold it between thumb and forefinger, and slide your fingers up the strand from the tip toward the root, against the cuticle. Low porosity hair feels smooth, because the cuticle lies flat. High porosity hair feels rough and bumpy, because the cuticle is lifted and damaged. Medium porosity feels smooth with a slight texture.
The test works because it measures the cuticle directly, not the water. A lifted cuticle is rough to the touch, and a flat cuticle is smooth, and no amount of product changes that in the moment. Do it on three strands from different parts of the head, because porosity varies: the ends are usually more porous than the roots, and heat-damaged sections are more porous than the rest.
What to do with the answer
Low porosity hair needs heat and light products. The cuticle resists water, so a shower cap and warm water help products get in, and heavy butters and oils sit on the surface and build up. Clarify more often, because buildup is the main problem, and use leave-ins that are thin, not thick.
High porosity hair needs the opposite: heavier creams, butters, and oils that seal the cuticle and slow moisture loss, and protein treatments that fill the gaps in the cuticle. The test that matters after you change products is the drying test: if the hair dries in under an hour, it is still losing water too fast, and the seal is not heavy enough yet.
Related reading
For the background behind “Hair Porosity: The Float Test, and What It Gets Wrong”, these earlier guides help: Leave-In vs Rinse-Out Conditioner: Same Ingredients, Different Job, Scalp Massage and Hair Growth: What the One Real Study Found, and Hair Serum in Brief: Silicone, Oil, and the Frizz Question.
Frequently asked questions
What is hair porosity?
How easily your hair absorbs and loses water, which depends on how flat or lifted the cuticle is. Low porosity hair resists water and product. High porosity hair absorbs fast and dries fast, and it loses moisture just as quickly.
Is the hair float test accurate?
No. Surface oils, conditioner, styling product, and hard water minerals all change whether a strand floats or sinks, so the test measures what is on the hair, not the hair itself. It also has no agreed time limit, and a low porosity strand will sink eventually.
How do I test porosity without the float test?
Slide your fingers up a single strand from tip to root. Smooth means low porosity, because the cuticle lies flat. Rough and bumpy means high porosity, because the cuticle is lifted. Test three strands from different parts of the head, because porosity varies.
What products work for high porosity hair?
Heavier creams, butters, and oils that seal the cuticle and slow moisture loss, plus protein treatments that fill the gaps. If the hair dries in under an hour, the seal is not heavy enough yet. Low porosity hair needs the opposite: light products and heat to help them in.