The Float Test in Brief: Why Porosity Tests Mislead

The float test mostly tells you whether the strand was clean, coated, or waterlogged before the test, not its true porosity. Hair that sinks has usually absorbed water because it was stripped or damaged, and hair that floats is often just coated with the oils and silicones from your last wash day.

What porosity actually is

Porosity is how readily hair absorbs and loses water, governed by the cuticle layer's condition. Raised, chipped, or missing cuticle, from bleach, heat, or weathering, lets water in and out fast. Intact, tightly laid cuticle slows both. It is a spectrum, and on one head it varies: ends are almost always more porous than roots.

That variation is the first problem for any single strand test. A shed strand from a brush is usually an older, longer, more weathered hair. Its behavior in a glass says little about the hair at your crown, which is where most product decisions are aimed.

Why the glass lies

Residue dominates the result. A strand carrying conditioner film or oil floats because the coating repels water, and gets labeled low porosity, when the label belongs to the product, not the hair. A strand washed in clarifying shampoo first can sink in minutes regardless of its cuticle state, because clean hair wets.

Water temperature, strand thickness, and how long you watch all move the outcome. A test whose result changes with the washing before it and the patience of the watcher is not measuring a stable property. It is measuring the afternoon it was performed on.

Tests that tell you something usable

Watch your own hair instead. How long does it take to get fully wet in the shower, and how long to air dry? Hair that wets instantly and dries in an hour behaves porous. Hair that resists wetting and stays damp all evening behaves resistant. That is the same information, gathered at the scale that matters, your whole head.

Product response is the other real test. If protein heavy products leave your hair stiff and straw like, treat it as sensitive to protein whether or not it is porous. If conditioners sit on top and never seem to absorb, clarify first before buying anything labeled for low porosity.

What to do with a porosity label anyway

Use it as a starting guess for product weight and nothing more. Heavier creams and butters for hair that drinks product and still feels dry. Lighter, more water based products for hair that gets weighed down and coated. Then let the second wash day overrule the label.

The brief version: your hair's behavior with water and product, observed over two or three washes, is a better porosity test than any glass of water. The strand in the glass cannot argue back, which is exactly why it feels so convincing.

Frequently asked questions

Is the float test ever accurate?

It can hint at very damaged, stripped hair that sinks fast, but coatings and preparation swing the result so widely that it should never be the sole basis for buying a routine.

Can porosity change over time?

Yes. Chemical services, heat, sun, and age raise porosity, especially at the ends. New growth arrives at your natural porosity, which is why one head can need two strategies at once.

Does low porosity hair need protein?

Porosity and protein need are separate axes. Resistant hair often dislikes heavy protein early in a routine, but the deciding test is response: stiffness after protein products is the signal to back off, whatever the label.

How do I test porosity without the float test?

Time your wetting and drying on a normal wash day and note how conditioners behave after a clarifying wash. Those observations, repeated twice, classify hair more usefully than a strand in a glass.