The Strand Test Lies: Porosity Checks That Tell You Something Useful
The float test mostly measures whether the hair was clean and whether surface tension held it up, not the porosity of the shaft. Porosity matters, it changes how fast hair takes up water and how easily it loses it, but the useful tests are behavioural: how long your hair takes to get fully wet, and how long it takes to dry.
Why the glass of water fails
A shed strand placed on water often floats because surface tension supports it and because oils and product residue make the surface water repellent, whatever the shaft's condition. Sink it and the result can mean the cuticle is raised, or simply that the strand was clean and finally wetted through. The test gives a different answer before and after a clarifying wash on the same head, which is the definition of a test measuring the wrong thing.
Porosity itself is real and worth knowing about in broad bands. It describes how readily the hair fibre absorbs and releases moisture, shaped by the cuticle's condition: chemical processing, heat, and weathering lift and chip it, virgin hair keeps it flatter. The mistake is expecting a kitchen test to grade it precisely enough to choose products by, when the hair's own behaviour under water and air gives the same bands more honestly.
Two behaviour checks that hold up
Time to wet: in the shower, note how long your hair takes to become fully saturated rather than beading and shedding water. Hair that resists wetting for a full minute under running water behaves as low porosity for product purposes, whatever its history. Time to dry: hair that stays damp for many hours after washing, with no heavy product load, is holding water in a porous fibre. Track both across two or three wash days and the band you are in is rarely ambiguous.
Product response completes the picture. Conditioner that sits on top and leaves hair stringy suggests uptake is slow and heat or warm water during conditioning will help more than a richer product will. Hair that drinks conditioner yet feels dry by evening is losing moisture fast, and sealing and protein balance move up the list. Protein and Moisture in Curl Routines: Reading the Signs Instead of Guessing develops the protein side of that second pattern.
What to change once you know the band
Low porosity behaviour calls for warmth and patience: apply conditioner to wet hair under a shower cap for a few minutes so heat lifts the cuticle, choose lighter, water based leave ins, and clarify on schedule because products that absorb slowly also accumulate on the surface. High porosity behaviour calls for the opposite emphasis: richer creams, sealing oils or butters on the ends, gentler cleansing, and protein support where the fibre is damaged.
Porosity also varies along one head: ends are older and more weathered than roots, and a highlighted section behaves differently from the virgin hair beside it. Treat the bands as guidance per section rather than a single label for the whole head, and any test, including these, stops being a verdict and starts being a tool.
Keep reading: Protein and Moisture in Curl Routines: Reading the Signs Instead of Guessing When Humidity Drops: Adjusting a Curl Routine for Dry Winter Air Should you brush curly hair wet or dry?.
Frequently asked questions
Why does the float test give different results on different days?
Because it is sensitive to product residue, oils, and surface tension, all of which change with your last wash, while porosity changes slowly. A strand floats when the water cannot wet its surface. That is a cleanliness reading dressed up as a fibre reading, which is why the result swings.
How do I tell if my hair behaves as low porosity?
Watch the wetting time. Hair that beads water and takes a long time to saturate in the shower, and where conditioner tends to sit on the surface, behaves as low porosity. Warmth during conditioning and lighter, water based products usually work better than richer formulas for this pattern.
Can hair be high and low porosity at once?
Yes, routinely. Ends are older and more exposed than roots, and coloured or heat styled sections are more porous than untreated growth. Work in bands per section: richer, sealing care on the porous lengths, lighter handling near the roots, rather than one label for the whole head.
Does porosity change over time?
It increases with cumulative processing, heat, sun, and mechanical wear, because all of them chip and lift the cuticle. Virgin new growth starts lower. That is why a routine that suited your hair two years ago can drift out of fit even with the same products: the fibre itself has changed.