Curl pattern is the first thing most people learn about their hair, but it’s only one of several traits that decide how your hair behaves. Porosity, strand thickness and density often matter more when you’re choosing products. This guide explains each one and how to find yours.
Curl pattern: the 2a–4c system
The familiar chart of numbers and letters — 2 for wavy, 3 for curly, 4 for coily, with a, b and c showing how tight the pattern is — was popularized by stylists as a shorthand, not created by scientists. It’s useful for describing how hair looks, and that’s how we use it.
Researchers who classify curl objectively measure things like curve diameter, curl index and the number of waves and twists along a strand. One worldwide study used those measurements to sort hair into eight types and found a continuous range rather than neat boxes. In practice, most heads have more than one pattern — looser at the crown and tighter at the nape, for example. The hair type quiz looks at your wet curl shape, shrinkage and coil size, and tells you when you sit between two types.
Shrinkage
Coily hair can look much shorter than it really is. As curls dry, they spring up and can shrink to a fraction of their stretched length. Shrinkage is a sign of elasticity, not a problem to fix. It does matter when you measure progress: length levels are always judged on stretched hair, and the hair growth calculator converts shrunken measurements for you.
Porosity: how hair handles water
Porosity describes how easily water and products move into and out of the hair. Low-porosity hair has a tight, flat cuticle: it takes a while to get wet, dries slowly and tends to let products sit on top. High-porosity hair soaks up water quickly but loses it just as fast, and often feels dry and rough.
Some hair is naturally lower or higher in porosity, but damage changes it. Laboratory measurements show porosity rises as hair is damaged by chemicals or heat. That’s why relaxed, colored or frequently heat-styled ends often behave like high-porosity hair even when the roots don’t.
The popular float test — dropping a strand into a glass of water — is easy but unreliable, because oils, residue and surface tension affect whether a strand floats far more than its porosity does. The hair porosity test asks about drying time, product build-up and chemical history instead, and shows how confident the result is.
Strand thickness and density
These two are easy to mix up:
- Strand thickness is how wide each individual hair is — fine, medium or coarse. Fine strands are more fragile and usually need less heat and lighter products.
- Density is how many hairs grow on each patch of scalp. High density means a lot of hair; low density means more visible scalp.
You can have fine strands at high density or coarse strands at low density. Studies that count hairs on the scalp have found that average density varies between groups and individuals, so “a lot of hair” can mean many fine strands or fewer coarse ones. Density matters most when you’re buying extension hair or planning styles; thickness matters most for heat and protein.
Why type alone doesn’t decide your routine
Two people with 4c hair can need opposite routines. One with fine, low-porosity strands may find butters heavy and protein stiffening; another with coarse, high-porosity strands may need richer creams and occasional protein. Your scalp, chemical history and how often you use heat matter as well.
That’s why our tools pass your results forward. A good order is:
- The hair type quiz — find your pattern.
- The porosity test — learn how your hair handles water.
- The wash day routine builder — get a plan that uses both.
Reading your hair over time
Hair changes. Hormones, age, medications, color and heat can all shift texture and porosity. If your hair suddenly starts behaving differently — new dryness, a different curl pattern, more breakage — re-take the tests instead of assuming an old label still fits. And if the change comes with shedding, thinning or scalp symptoms, see a board-certified dermatologist.