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Hair Porosity Test: When the ‘cup test’ doesn’t work

Tried the hair porosity cup test and got confusing results? You’re not alone. The ‘cup test’ often doesn’t work — here’s why, how you can find your hair’s true porosity, and the best products for low and high hair porosity to build a routine that works.

Hair porosity test didn’t work for you? Don’t worry, it didn’t work for me either. I tried the ‘cup test’ over and over, without success. Here’s why, and what you can do insted.

Hair porosity is important because it determines how your hair absorbs and retains moisture.

It determines:

  • Which products work best for you.

  • How well your hair responds to hydration.

  • How long your styles last.

  • How prone your hair is to frizz, breakage, or buildup.

Basically, it’s key if you want to develop a routine that actually works for your hair type — especially for curly, dry, damaged, or colour-treated hair.

If you Google ‘hair porosity’, you’ll probably come across several videos and links to the cup test — drop a clean strand of hair into a glass of water. If it sinks, you have high porosity hair. If it floats, you have low porosity hair.

But that’s not necessarily correct. In my case, it was dead wrong.

Note: There are some product recommendations for different hair types in this post. I have not tested them all out because they won’t all work for my hair type, but I have checked the ingredients of each one to make sure they’re quality products. There are also some affiliate links below — clicking on them does not cost you anything extra, it just helps me keep the site running :)

Hair Porosity Cup Test

What is hair porosity?

Porosity refers to how open or closed your hair’s cuticle layer is — that’s the outermost layer made of overlapping cells (like roof shingles).

  • Low porosity hair has tightly packed cuticles. Moisture takes longer to get in, but it also stays in longer.

  • High porosity hair has raised or damaged cuticles. It absorbs moisture quickly, but loses it just as fast.

  • Medium porosity falls somewhere in the middle — a balance between absorption and retention.

    Hair porosity can also change. Cuticles can open with age, which means you might need to start using heavier products.

    Damage from bleach and dye can also cause your hair to become high porosity — this can usually be reversed by growing the dye out and going back to natural hair, or using low-damage colour. It’s always best to ensure your hair is healthy and in good condition before you use colour.

    What happened when I tried the cup test

    I have fine hair that is quite dry at the ends, but hydrated closer to the root. Every time I tried the cup test, the strand floated on top of the water. Every. Single. Time. According to the cup test, that means I have low porosity hair that does not absort moisture easily.

    Except I don’t have low porosity hair. It has never struggled to absorb moisture, but it does get overloaded with product easily.

    I’ve tried the cup test a number of times over the years with long strands, short ones, dyed ones, even grey ones. I once washed a solo strand of hair and dried it to ensure the cuticles were not sealed when I dropped it ino the cup.

    It didn’t matter what I did, the strand aways floated. The last time I tried it, I decided to break the surface tension of the water by poking the hair just under the surface. The strand became a bit waterlogged and didn’t reach the surface again. It stayed where I poked it, hovering just below the surface.

    I knew the strand test was’t working for me, but I didn’t know why.

Low porosity hair - tighly packed cuticles, retains moisture.

Medium porosity hair example

Medium porosity hair - tends to stay hydrated with regular washing.

High porosity hair - dry appearance, needs heavy products.

The problem with the cup porosity test

It measures water density, not cuticle structure.

Whether the hair strand sinks or floats can be influenced by:

  • Whether the strand has product or oil residue.

  • The temperature and type of water.

  • Air bubbles clinging to the hair.

  • The thickness or length of the hair strand.

Clean, healthy hair can sometimes sink. Damaged hair can sometimes float. The results are too inconsistent to be useful.

In my case, my strands are too fine to do anything but float on the surface. Even if they were high porosity, my strands were never going to sink.

A better way to test hair porosity

You don’t need a glass of water to understand your hair. You just need to look at how it responds to moisture and product.

Wet feel test

After you wet your clean hair:

  • If water seems to sit on the surface, or beads, and takes a while to absorb, you may have low porosity hair.

  • If your hair drinks up water quickly but still feels dry soon after, it may be high porosity.

  • If it absorbs water easily but doesn’t feel overly dry or saturated, it’s probably medium porosity.

Drying time test

Pay attention to how long your hair takes to dry without any product:

  • Low porosity hair takes a long time to dry.

  • High porosity hair dries quickly, often unevenly.

  • Medium porosity dries relatively evenly, in a moderate amount of time.

Drying time is one of the easiest and most reliable ways to assess porosity at home.

Product absorption test

How your hair reacts to leave-ins, oils, or conditioners can also reveal clues:

  • Product sits on top or takes forever to absorb? Likely low porosity.

  • Product disappears quickly but doesn’t feel moisturised for long? Likely high porosity.

  • Holds styles well and reacts predictably to products? Likely medium porosity.

The stretch test

Take a wet strand and gently stretch it:

  • If it stretches and returns: balanced moisture and elasticity

  • If it stretches and breaks easily: often a sign of high porosity or damage

  • If it barely stretches and feels stiff: may be low porosity, protein overload, or dehydration

    I worked out my hair is mostly medium porosity, but it turns into high porosity at the ends. I know that because the first 3/4 of the length reacts predictably to product and naturally remains pretty moisturised.

  • The ends can be wirey - they quickly absorb oils, unlike the rest of my hair, they dry much faster than the rest of my hair, and they lose moisture quickly.

  • No, it’s not a reliable method. It doesn’t reflect how your hair behaves or how your cuticle layer is structured.

  • Use real-world observations: how your hair dries, feels when wet, and absorbs product. These are much more accurate indicators of porosity.

  • Yes. Many people have mixed porosity — especially if parts of their hair are coloured, damaged, or exposed to more sun or heat than others.

What to do once you know your porosity

Once you’ve identified your hair’s porosity, you can tailor your routine to support it.

For low porosity hair

  • Use lightweight, water-based products.

  • Apply heat (like a warm towel or steamer) to help open the cuticle during deep conditioning.

  • Avoid heavy butters and oils that may sit on the surface.

  • Clarify gently every few weeks to prevent buildup.

For high porosity hair

  • Focus on moisture retention: rich conditioners and sealing oils.

  • Use protein-based treatments (in moderation) to help strengthen and fill cuticle gaps.

  • Try layering techniques like LOC (liquid, oil, cream) to lock in hydration.

  • Be gentle when detangling and avoid harsh heat or chemical treatments.

    For medium porosity hair

  • Use a gentle shampoo and lightweight conditioner regularly.

  • Moisturise as needed, but avoid heavy layering unless your hair feels particularly dry.

  • Incorporate deep conditioning occasionally (every two to four weeks).

  • Use protein treatments only as needed — for example, after colouring, heat styling, or seasonal changes.

  • Watch for signs of buildup or imbalance, especially if your routine changes.

Final thoughts

The float test for hair porosity is popular online, but it’s not reliable. While it seems like a quick fix, it often leads to confusion — and the wrong product choices.

Instead, observe your hair:

  • How long it takes to dry.

  • How it feels when wet.

  • How it reacts to products.

Those everyday cues are much more useful than watching a hair strand in a glass of water. By tuning into your hair’s real behavior, you’ll build a routine that actually works.

Did the cup test work for you, or do you have a different method? Let me know in the comments below!

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