First... What the Hell Is Hair Porosity? 🔬

Let's rescue the science before we drag the glass. 

Hair is not an impermeable piece of plastic. Water can interact with the fiber, and researchers can study properties including water sorption, swelling, surface wettability and structural porosity under controlled conditions.

So when people talk about hair being more or less porous, there is legitimate fiber science underneath the beauty terminology.

The problem begins when a complex subject gets compressed into three extremely confident sentences:

No examination of the fiber. No investigation of what's on it. No controlled measurement.

The Viral Float Test: What Are We Actually Doing? 🥛

The popular version usually goes like this:

Put a clean strand of hair into a glass of water. If it remains near the surface, call it low porosity. If it stays somewhere in the middle, call it medium porosity. If it sinks toward the bottom, call it high porosity.

The explanation commonly attached to the test is that highly porous hair supposedly takes in water more readily and sinks, while less porous hair supposedly resists water and stays afloat.

Beautifully simple.

Maybe a little TOO beautifully simple. 👀

Wait... Why Would a Hair Float in the First Place?! 😳💧

A tiny fiber sitting on water is part of a physical system. There is the hair itself, its dimensions and surface chemistry, the water, the air-water interface and the question of how effectively water wets the fiber.

Researchers can examine hair-surface wettability with controlled measurements such as water contact angles rather than simply watching where one random strand eventually lands in a drinking glass.

Hello, Surface Tension 👋💧

At the air-water interface, water behaves differently from water deep inside the glass. For a tiny lightweight fiber interacting with that interface, the initial contact with the surface matters.

So before seeing a strand remain at the top and announcing “LOW POROSITY!”, there is a more basic question:

Did the strand actually become completely wetted?

Remaining near an air-water interface is an observation. It is not, by itself, a complete measurement of the internal structure of that hair fiber.

Wait... Did the Hair Even Get Completely Wet?! 👀

Touching water and being fully wetted by water are not necessarily the same event.

Relatively intact hair has a lipid-containing exterior that contributes to surface hydrophobicity. Chemical processing such as oxidative bleaching can alter that surface and change its interaction with water.

Yet the viral interpretation often skips all of that and jumps directly from the strand's location to an identity:

No ma'am. We have more questions.

And What  Is Already on That Hair?! 🧴😂

Is the fiber entering that glass actually bare?

Or has it recently met conditioner, leave-in, serum, hair oil, styling cream, dry shampoo, hairspray, sebum or another cosmetic deposit?

Conditioning products are specifically designed to interact with and coat hair surfaces. That means the strand you are testing may have a surface condition influenced by both the hair itself and the products it has encountered.

“Okay... Then I'll Wash the Hair First!” 🚿

Reasonable thought.

But notice what happens when you cleanse the strand: you may change the oil, sebum or cosmetic material present on its surface.

In other words, you have changed the experimental conditions.

That doesn't automatically turn the float test into a controlled porosity measurement. Instead, it reminds us that surface condition matters.

One Strand?! From WHERE?! 😳🔬

You pulled out one hair.

Okay. WHICH HAIR? 

Was it from the crown? The front? An underneath section? A highlighted area? A section repeatedly exposed to a flat iron?

Hair fibers from one head do not necessarily share identical treatment and exposure histories.

And then we get to the really fun part:

Your Roots and Your Ends Have Not Lived the Same Life 

The fiber close to your scalp is relatively new.

Your long ends?

THOSE GIRLS HAVE STORIES. 

Older lengths may have experienced more washing, brushing, combing, sunlight, friction, heat styling, coloring, bleaching and environmental exposure.

That cumulative history is one reason long hair can show different surface condition along its length.

Bleaching Can Absolutely Change the Story 🧪

Chemical processing is one reason the real science of hair porosity is far more interesting than the glass.

Oxidative bleaching can alter the cuticle, surface lipids and other structural characteristics of the fiber. Controlled studies have measured corresponding changes in hair wettability.

X-ray microtomography has also been used to quantify pore volume in differently treated hair fibers—an actual structural measurement rather than a visual guess based on where one strand sits in water.

What About the Size of the Hair? 🤏

Hair fibers are not physically identical.

Diameter and other characteristics vary between people and among fibers. So a strand's behavior in water occurs within a system containing more variables than one abstract label called “porosity.”

That does not mean diameter alone tells us whether a strand will float or sink.

It means we should be careful about pretending porosity is the only possible variable involved.

This Isn't a Controlled Lab Test 🔬🥛

Imagine submitting this methods section:

Science would have QUESTIONS.

Controlled experiments define their materials, preparation, treatment conditions, measurement techniques and endpoints.

So... Does the Float Test Tell You Absolutely Nothing? 👀

We don't need to make that claim either.

Watching how a fiber interacts with water can be an interesting observation. The problem is giving the observation more precision than it has earned.

If one strand remains near the surface, the direct observation is:

What has not automatically been established is that every fiber on your head has been precisely diagnosed as low porosity and therefore requires a predetermined product collection.

That's a LOT of promotion for one little hair. 😂

So How Do Scientists Actually Study This Stuff?! 🔬

Depending on the research question, scientists can investigate hair using microscopy, water-sorption measurements, swelling measurements, contact-angle testing, mechanical testing and structural imaging techniques.

Different methods answer different questions.

For example, contact-angle testing can examine surface wettability, while X-ray microtomography can provide information about structural pore volume within fibers.

Are “Low, Medium and High Porosity” Useful at All?

They can be useful as consumer shorthand.

The trouble starts when we treat them like three permanent biological species of human hair. 

Hair condition can vary with chemical processing, environmental exposure, cumulative weathering and location along the fiber.

Use porosity language as one way of thinking about hair behavior—not as an identity card that overrides everything else you know about your hair.

And Now We Get to the Product Prescription Problem 🧴😳

This is where the cute experiment can suddenly become expensive.

Your strand floated? Buy the low-porosity collection.

It sank? You apparently need an entirely different shelf.

WAIT.

Finished hair products are formulations, and how they perform can depend on hair type, fiber condition, chemical history, cleansing routine, styling goals, amount applied and the other products being layered with them.

Even the American Academy of Dermatology recommends considering hair type when selecting hair-care products and adjusting care according to factors such as oiliness, dryness, texture and chemical or heat exposure.

Then What Should I Actually Pay Attention To?! 👀

Patterns.

Start with your hair's real history and repeated behavior:

The goal is not to replace the float test with another simplistic home diagnosis.

It's to build a more useful picture from repeatable behavior + hair history + the actual problem you're trying to solve.

The Hair Porosity Reality Table 🥛🔬

There. The glass may now return to making mojitos. 🍹

Wait... Where Does Split Ender Fit Into This? ✂️🥛

Porosity ≠ split ends.

Porosity discussions concern characteristics of the hair fiber and how it interacts with substances such as water.

A split end is physical separation or fraying at the terminal hair shaft. These issues can coexist, but they are not interchangeable diagnoses.

Split Ender's role is different: when used as directed on clean, dry, detangled hair, small sections are guided through its guarded chamber so the trimming system can address tips that enter the cutting area while helping preserve the overall appearance of length.

It does not diagnose porosity. It doesn't turn “high porosity” into “medium porosity.” And it doesn't decide what conditioner belongs in your shower.

Don't Let One Hair Run Your Life 😂

Hair porosity isn't fake.

Hair-water interaction isn't fake.

Chemical processing can absolutely change hair structure and surface behavior.

And that is precisely why the subject deserves more respect than:

If you enjoy doing the float test, observe it. Get curious. Have fun with it.

Just don't give one strand in one household glass the authority of a complete laboratory characterization of every fiber on your head.

Your hair has history. Different zones can have different histories. Products can alter the surface. Chemical treatments can alter the fiber. And your hair's repeated behavior during your real routine gives you context that one little swimming competition cannot capture.