Porosity is the most underrated word in curl care. It's the difference between a routine that works and one that leaves your hair feeling like straw despite pricey products. This is the full UK guide to testing your porosity, understanding the cuticle anatomy behind it, and matching your routine to UK water hardness and humidity — three factors that move porosity around throughout the year.
What is hair porosity?
Porosity is your hair's ability to absorb and retain moisture — controlled by the cuticle, the outermost layer of the hair shaft. The cuticle is made of overlapping scales (like roof tiles) that lie flat in healthy hair. When the scales lie tight and flat, water and product struggle to get in or out — that's low porosity. When the scales are lifted and damaged, water and product enter and exit the shaft easily — that's high porosity.
Curly hair averages higher porosity than straight hair because the curl pattern itself causes natural lifting at the bends in each strand. Type 4 hair has the highest baseline porosity for this reason.
The 5-grade porosity scale
Most charts simplify porosity to "low/medium/high" but the more useful clinical scale (used by the American Board of Certified Hair Colorists and adopted by Curlsmith) is a 5-grade system:
- 1 — Resistant porosity: Cuticle so tightly closed that even chemical processes struggle. Rare; common in virgin Asian hair.
- 2 — Low porosity: Cuticle flat and closed. Water beads on the surface. Hair takes ages to wet through and ages to air-dry.
- 3 — Normal porosity: Healthy balance. Wets within minutes, dries in reasonable time, holds moisture without product overload.
- 4 — High porosity: Cuticle slightly raised. Wets fast, loses moisture fast. Frizzy ends, tangles easily.
- 5 — Extreme porosity: Cuticle severely damaged or missing. Hair is over-processed, bleached, or heat-damaged. Often needs trimming, not products.
The three porosity tests
1. The float test
Take a single clean, product-free strand from your brush. Drop it into a glass of room-temperature water. Wait 5 minutes.
- Floats: low porosity
- Sinks slowly to middle: normal porosity
- Sinks immediately: high porosity
The float test gets criticised because oils and sebum on the strand can cause false positives. Make sure the strand is freshly washed and rinsed.
2. The spray test
Mist a section of clean, dry hair with a spray bottle. Watch what happens.
- Water beads on the surface: low porosity
- Absorbs after a few seconds: normal
- Absorbs immediately, hair feels damp throughout: high
3. The slip test
Slide a single strand between two fingers, from root to tip and back to root.
- Smooth both directions: low
- Smooth root-to-tip, slight resistance tip-to-root: normal
- Resistance both directions, feels rough: high
Signs of low porosity hair
- Takes 5+ minutes to fully wet through under the shower.
- Products sit on the surface; conditioner washes out without absorbing.
- Air-drying takes hours.
- Hair feels coated or builds up easily.
- Heat treatments (heat caps, steamers) make a noticeable difference.
Signs of high porosity hair
- Wets through almost immediately.
- Conditioner absorbs fast — feels good wet, dry by lunchtime.
- Tangles easily, especially at the ends.
- Frizzy in any humidity.
- Often colour-treated, bleached, or heat-styled.
Signs of medium/normal porosity hair
- Wets through in 30 seconds to 2 minutes.
- Holds curl pattern well throughout the day.
- Tolerates a wide range of products without obvious build-up or dryness.
- Air-dries in reasonable time.
What changes your hair porosity
Porosity isn't fixed — it shifts throughout your life and with the seasons. Things that raise porosity (damage the cuticle):
- UVA/UVB exposure: oxidises the cuticle. Worse in summer.
- Pollution: particulate matter abrades the cuticle. Worse in cities (London, Manchester, Birmingham).
- Heat styling above 160°C: denatures keratin, lifts cuticle.
- Bleach and high-lift colour: chemically lifts cuticle.
- Hard water: calcium and magnesium build up on the cuticle.
- Chlorine: oxidises cuticle. Swimmers — rinse before and after.
Things that maintain low/normal porosity:
- Sulphate-free cleansing.
- Apple cider vinegar rinses (smooths cuticle).
- Cool-water final rinses.
- Bond-builders (e.g., Curlsmith Bond Curl Rehab Salve).
- UV protection in summer.
UK water hardness × porosity lookup
The UK has the most varied water hardness of any country in Europe. Where you live matters.
| Region | CaCO₃ (mg/L) | Hardness | Clarify cadence |
|---|---|---|---|
| London / SE England | 250-350 | Very hard | Every 2-3 weeks |
| East Anglia | 200-280 | Hard | Every 3 weeks |
| Birmingham / Midlands | 150-250 | Moderately hard | Every 4 weeks |
| NW England / Wales / SW | 60-120 | Soft to moderate | Every 5-6 weeks |
| Scotland / Cornwall | < 60 | Very soft | Every 6-8 weeks |
Hard water raises porosity over time — the calcium and magnesium ions deposit on the cuticle and oxidise the strand, especially with chlorinated tap water. London and South East curlies need more frequent clarifying than Scottish curlies. Water UK publishes regional hardness data by postcode if you want to check yours specifically.
For UK clarifying, the Bounce Curl Gentle Clarifying Shampoo removes mineral build-up without stripping curl pattern. Use according to your regional cadence above.
Porosity × curl pattern combo matrix
| Combination | Common needs | Avoid |
|---|---|---|
| 3A low-porosity | Lightweight water-based products, deep condition with heat | Heavy butters, coconut oil, protein |
| 3A high-porosity | Layered moisture, sealing oils, weekly protein | Hot water washes, sulphates |
| 3B low-porosity | Steam treatments, mid-weight leave-ins | Heavy creams that won't penetrate |
| 4A low-porosity | Steam, lightweight leave-ins, gentle protein monthly | Heavy butters, mineral oil |
| 4C high-porosity | LOC method, weekly protein, heavy butters and sealing oils | Drying alcohols, sulphate cleansers |
Seasonal UK humidity calendar
Dew point (the temperature at which moisture condenses out of the air) determines whether humectants like glycerin work for or against your hair.
- Dew point above 15°C (UK summer mornings, July-September): humectants pull water into the hair. Good for low-porosity hair, bad for high-porosity (frizz).
- Dew point 5-15°C (UK spring/autumn): humectants behave neutrally.
- Dew point below 5°C (UK winter, December-February): humectants pull water out of hair. Switch to anti-humectants (gels, polymer-based stylers).
Met Office UK climate data publishes monthly dew-point averages by region.
Porosity drift — how heat, colour, sun shift your porosity
Your porosity isn't a permanent label. Test monthly — especially after:
- Heat-styling for an event (one-off thermal damage).
- Beach holiday (UV + chlorine).
- Hair colour appointment.
- Major lifestyle change (new water region, new climate).
Keep a quick log if you find your products stop working — usually it's porosity drift, not a "bad product."
Building your routine by porosity
For full routines:
- Low porosity: see our low porosity hair routine guide.
- High porosity: see our high porosity hair guide.
- Pre-wash scalp prep for either: Kitsch Pre-Wash Scalp Oil with Rosemary & Biotin.
- Gentle daily cleanse: Innersense Hydrating Cream Hairbath.
FAQs
Can I have low porosity at the roots and high at the ends?
Yes — extremely common. Roots are newer hair (less damage exposure); ends have lived through more heat, sun, colour, and friction. Adjust products by section.
Does the float test actually work?
It's a directional indicator, not a clinical measure. The strand needs to be freshly washed and rinsed for the result to be meaningful. False positives happen if oil is on the strand.
How often should I deep condition for high porosity?
Twice a week minimum, weekly under heat. High porosity loses moisture fast — you're constantly replenishing.
Will protein damage low porosity hair?
Overuse can. Low porosity hair often doesn't need much protein because the cuticle is intact. Once a month is usually plenty.
Why do my products work in summer but not winter?
Dew point shift. Humectants in your styler that draw water into hair in humid summer pull water out of hair in dry winter. Swap to anti-humectant formulas in winter.
Take the porosity quiz
Use our AI Hair Analyser for an instant porosity + curl type diagnosis from a photo.
Author: Emma Rusby, Founder of Zenvy Beauty. UK curl-care specialist.
