The answer is texture. Texture is the term for how coarse or fine an individual strand is, measured by its diameter.
Density, porosity, and elasticity are separate hair properties tested on their own — density counts how many strands grow per square inch, porosity is how well the cuticle absorbs moisture, and elasticity is how far a strand stretches before it breaks. Texture is strictly about strand thickness, and it can even vary across different spots on the same head.
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