Hair porosity test
Porosity is how easily water gets into and out of the hair shaft. It decides whether heavy oils help you or leave hair greasy, and why a product everyone praises does nothing for you.
Porosity is not fixed: bleaching, straighteners and hard water raise it over time. Coloured hair is almost always more porous than virgin hair, whatever the other answers say.
Frequently asked questions
Is the glass-of-water test reliable?
Not on its own. Product residue or sebum on the strand changes the result. That is why it is one of five questions rather than the whole test.
Can porosity change?
Upwards, easily — any damage raises it. Downwards only in appearance, through products that temporarily close the cuticle; the strand itself does not repair.
Which matters more, porosity or strand thickness?
Porosity decides what the hair absorbs, thickness decides how heavy a product can be before it goes limp. They are read together.