Hair Porosity TestQ: How do you carry out a porosity test and how can you see the difference between "good" and "bad" porosity?
A: The simplest way to test the porosity of the hair is to get a spray bottle with water that will generate a fine mist. You also need to start with clean, dry hair with no product in it. (Preferably hair that was shampooed the night before as blow drying can leave the cuticle swollen and will make the hair seem more porous.)
Simply comb a segment of hair and hold it in hand, then holding the sprayer at least 6-8 inches away, spritz the hair and watch the way the water reacts with the hair. If the water is immediately absorbed and disappears then the hair is porous. If the water beads up or begins rolling off the hair immediately, the hair is non-porous (what we call resistant).
Porosity is a measure of the compactness of the cuticle layer of the hair. When the cuticle is raised (often a sign of hair damage) moisture (water) passes easily in and out of the hair shaft, with the end result being that the hair feels dry and rough, and looks frizzy. Porous hair tends to process chemical reactions quickly and can therefore over-process easily in many cases, so must be carefully and closely monitored.
A compact cuticle is one whose cuticle scales are tightly closed - which happens often when the hair turns gray - and is what we term as resistant hair. Resistant hair is harder to process and may need to be pre-softened (have the cuticle opened a little) in order to get good color results. Resistant hair also resists things like conditioners and protein treatments.
"Normal" hair (what we most desire to find) is that the spray test leaves small beads of water on the hair at first, but that the water is absorbed after a moment. This generally shows a cuticle that is smooth and flat but not so tight as to prevent penetration by desired products.
Both ends of the porosity spectrum are problematic, although the problems of VERY porous hair can be devastating if not addressed and handled very gently. When the hair has been severely damaged so that the hair is overly porous, you can generally identify that there's a problem by the fact that when dry, the hair feels like straw, and instantly soaks up any moisture it encounters. Yet, when the too-porous hair is wet, it feels spongy and unpleasantly rubbery.
Good porosity is a matter of balance. It's the sign that the hair is healthy, and that the cuticle layer is doing its job of regulating the moisture level in the hair.
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