Porosity: Hair’s ability to absorb and retain moisture

What is Porosity?

Porosity is a hair property that measures how well your hair can absorb and hold onto moisture and products. Think of it like a sponge—some sponges soak up water fast, while others barely get wet.

Your hair’s porosity is determined by the condition of its outer layer, called the cuticle. Most people miss this: your porosity can change over time due to damage, and it’s the single biggest factor in why your favorite product might work for your friend but not for you.

Why Porosity Makes or Breaks Your Hair Routine

Your hair’s porosity decides everything. It controls if moisture gets in, stays in, or just sits on top. High porosity hair acts like a cracked cup, leaking everything you put in.

Low porosity hair is like a plastic bag, sealing water out. I see this when patients complain their hair is always dry or their conditioner just slides off. They’re fighting their porosity.

Think of your cuticle layer like shingles on a roof. When they lie flat, it’s hard for water to penetrate. When they’re lifted or damaged, water floods in and escapes just as fast.

When Low Porosity Locks Out Moisture

Low porosity hair has cuticles that are tightly bound and lie very flat. This creates a smooth, resistant surface. Water and products bead up on it instead of soaking in.

Your hair often takes forever to get fully wet and even longer to air dry. Heat can help slightly lift those cuticles to allow absorption. I tell my clients with this type to use warm heat caps during deep treatments.

Never combine heavy oils or butters as your first step on low porosity hair—it causes instant buildup and dullness in my clinic. You must use lightweight, liquid-based products first.

The High Porosity Sponge Effect

High porosity hair has gaps and holes in its cuticle layer from chemical processing, heat, or environmental damage. It absorbs water instantly but can’t hold onto it.

Your hair often feels dry shortly after washing and tangles easily because the rough cuticles catch on each other. Think of it like a sponge full of holes.

80% of my clients with high porosity hair misunderstand protein. They overload on it, but what they really need are sealants and humectants used in a specific order to lock moisture in.

The Porosity Test You Can Do at Home

The float test is simple. Take a few clean strands from your brush and drop them into a glass of room-temperature water. Watch what they do for 2-4 minutes.

If the hair sinks quickly, it’s likely high porosity, soaking up water. If it floats for a long time, it’s likely low porosity, resisting absorption. Hair that floats midway is average porosity.

This test isn’t perfect, but it’s a great starting point. In my practice, I combine this with a tactile feel of the strand and a case history for a full assessment.

From My Experience

The biggest insight I share is that porosity isn’t static. I’ve tracked clients’ porosity changing after a single bleaching session or after a year of consistent protective styling.

You can manage it. For high porosity, I prescribe a “layer and seal” method: a light leave-in conditioner followed by a cream, then a butter or oil to seal. For low porosity, it’s “heat and liquid”: warm water rinses and water-based products only.

Most importantly, listen to your hair more than the trend. If a popular hair mask makes your hair feel like straw, your porosity is telling you it’s wrong. Your hair’s behavior is the best diagnostic tool you have.