The number
was never
the whole story.

The Walker system was originally created to market a product line — not to provide clinical hair care guidance. It categorized hair by its visual curl pattern and assigned numbers and letters to those patterns. It said nothing about whether the hair was porous or resistant, dense or sparse, fine or coarse. It said nothing about what the hair needed, how it behaved with products, or how it responded to chemical and thermal stress.

And it carried biases that compounded the gap — implicitly positioning straighter textures as more manageable, originally leaving the tightest coil patterns without adequate representation, and suggesting that type 4 hair should simply be relaxed rather than understood and cared for on its own terms.

The result was a generation of consumers who knew their curl type number but had no clinical framework for understanding why their hair behaved the way it did — or why products worked for someone with the same number but not for them.

Two people both identified as 4C could have completely opposite hair care needs. One with low porosity, fine strands, and low density requiring lightweight penetrating products. Another with high porosity, coarse strands, and high density requiring rich occlusives and protein repair. The typing system gave them the same label and sent them toward the same products. One thrived. One didn’t. Neither understood why.

Understanding three additional characteristics — porosity, density, and strand width — gives you the complete clinical picture of what your hair truly needs. The curl type tells you what your hair looks like. These three tell you how it behaves, what it can receive, and how much stress it can handle.

1. Porosity.

   How well your hair absorbs and retains moisture.

   Porosity is determined by the condition of the cuticle — the outermost protective layer of every hair strand. Think of the cuticle like shingles on a roof. When those shingles lie flat and tightly closed, moisture struggles to get in. When they are raised or damaged, moisture enters easily but escapes just as fast.

   High porosity hair absorbs products quickly but loses moisture just as rapidly — leaving hair that feels dry within hours of moisturizing. This is common in hair that has been chemically treated, heat styled frequently, or exposed to significant environmental stress. Low porosity hair resists moisture entry — products sit on the surface rather than absorbing, and the hair takes longer than expected to get fully wet in the shower. Medium porosity hair sits between the two — absorbing and retaining moisture predictably with fewer interventions needed.

   Diagnostic at home

   The slip-and-slide test.

   Take a single shed strand and slide your fingers slowly from the tip toward the root, against the direction of hair growth. If the strand feels smooth with little resistance, your cuticle is flat and tightly closed — low porosity. If it feels rough, bumpy, or catches on your fingers as you slide, your cuticle is raised — high porosity. If there is slight texture but no significant roughness — medium porosity.

   Test strands from three different areas — your hairline, crown, and nape — because porosity often varies across the head and along the length of a single strand. The ends of your hair have been exposed to more cumulative damage than the roots and are almost always higher porosity on the same head.

   Knowing your porosity helps you choose products and techniques that work with your cuticle rather than against it.

2. Density.

   How many strands you have.

   Hair density refers to the number of strands growing from the scalp per square inch. It is frequently confused with strand width — how thick each strand is — but the two measure completely different things. Density is divided into three levels: low, medium, and high.

   High density hair has more strands per square inch, creating the appearance of fullness and volume. Low density hair has fewer strands with more visible scalp, particularly at the part line. Medium density falls between the two.

   Diagnostic at home

   The ponytail circumference test.

   Pull your hair into a low ponytail at the nape of your neck on dry, product-free hair and measure the circumference with a soft measuring tape.

   Under two inches indicates low density. Two to four inches indicates medium density. Over four inches indicates high density.

   Density influences everything from product quantity to styling approach. High density hair requires more product to ensure even distribution across more strands and thorough cleansing to prevent buildup trapped close to the scalp. Low density hair needs lighter products that do not weigh down the limited strands or reduce the appearance of volume — heavy creams and butters that work beautifully on high density hair can make low density hair look flat and sparse.

3. Strand width.

   The diameter of each individual hair strand.

   Strand width refers to the thickness of a single hair strand — categorized as fine, medium, or coarse.

   Fine strands have a smaller diameter and a smaller cortex — the protein-filled core that gives hair its strength and elasticity. Less cortex means less structural resilience against breakage, heat, and chemical stress. Fine strands reach damaging temperatures faster under heat tools, are more sensitive to protein overload, and collapse under heavy products more easily than any other width. Coarse strands have a larger cortex and significantly more structural resilience but a more resistant cuticle that makes moisture penetration harder — requiring richer products and deeper conditioning to stay pliable. Medium strands fall between the two and are the most forgiving of the three.

   Diagnostic at home

   The roll test.

   Take a single shed strand and roll it slowly between your thumb and index finger.

   Coarse hair can be distinctly felt with clear resistance. Medium hair has a slight but definite presence between the fingers. Fine hair is barely perceptible — you may struggle to feel it at all.

   Many people assume their hair is difficult when in reality they have been using products formulated for a completely different strand width. A fine-strand client reaching for rich butters because they want more moisture, or a coarse-strand client using lightweight wavy-hair products because they want more definition, is actively working against their hair rather than with it.

The Walker typing system tells you what your hair looks like. Porosity, density, and strand width tell you what your hair needs. One describes the pattern. The other explains the behavior. For too long, only one of them existed in the consumer conversation.

These three characteristics are not competing with the typing system — they complete it. The curl type gives you a starting point and a shared community language. The clinical framework gives you the precision to actually act on it.

Consider two clients with the same coily type 4 hair. One has low porosity, low density, and fine strands. The other has high porosity, high density, and coarse strands. Same curl type number. Same community category. Completely opposite hair care needs. The same products applied to both will produce different results — and on the first client, the products designed for the second may cause real damage.

Porosity tells you what the hair can receive. Density tells you how much product it needs. Strand width tells you how much stress it can handle. Together they give you the full clinical picture that a curl type number alone could never provide.