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| Ken and his plastic hair. |
One of the greatest differences for medium to coarse hair vs. fine hair is an element of flexibility. In cosmetics science, it is sometimes called plasticity.
This isn’t about plastic hair (but I can’t resist a photo of Ken, Barbie's anatomically ambiguous "friend"). Oils, conditioning agents like cationic quaternary surfactants (your conditioner probably has them), fatty alcohols like cetyl alcohol and “butters” like shea butter and silicones all add plasticity to hair. So might proteins, amino acids and humectants.
This isn’t about plastic hair (but I can’t resist a photo of Ken, Barbie's anatomically ambiguous "friend"). Oils, conditioning agents like cationic quaternary surfactants (your conditioner probably has them), fatty alcohols like cetyl alcohol and “butters” like shea butter and silicones all add plasticity to hair. So might proteins, amino acids and humectants.
When we think “plastic” in everyday life, we usually think of hard or semi-hard plastic boxes and containers. But in biology, physics and engineering, “plasticity” means the object in question has flexibility, it can be molded (deformed) and is pliable. In this post, I suggested that one of the troubling issues for fine hair is that it can have an excess of plasticity – it is very easily deformed.
Hair which is coarse (the diameter of the hair shaft), or which has a determined wave/curl to it, resists deforming under a load. It is not as super-flexible as fine hair. Hair which is kinking – has little bends and twists of the actual hair shaft, not just a simple, general curling habit, also tends to lack plasticity. So fine / medium hair and coarse hair are very different fibers. Kinking, curly fine hair and curly fine hair without kinks are quite differently-behaving fibers. Fundamentally, they are made from the same ingredients, but the expression of the ingredients is different.
If hair is low on plasticity, it is difficult to change it’s shape – hard to curl straight hair, hard to straighten curly hair. It will tend to feel thick and strong rather than silky. It will behave differently in a variety of situations and to a variety of treatments. It may not want to lie smoothly, which is a prerequisite for shine.
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| Fine hair, like coiling up cotton rope, bends willingly |
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| Medium to wide hair resists bending, rather more like coiling up a garden hose. |
Coarse hair has more internal support than fine hair. It holds it’s own shape quite well, it is less likely to be weighed down. It isn’t easily dented by ponytail holders and bobby pins. You can see in the graphic (below) how much more brown (hair cortex) there is with a wider hair than a narrower (fine) hair. This is why wider hairs are less pliable. I like to imagine fine hair like trying to wind or coil up a cotton rope and wide hair like coiling up a garden hose, which resists the bending and tends to want to coil in it’s usual pattern.
In the fine hair post, this visual aid represented the problem of how much more conditioner or oil clings to fine hair vs. wider hairs, relative to the mass or volume of the interior of the hair. It works the other way around for wider hairs or kinky hairs – plenty of conditioner is needed to make this hair type feel soft and smooth and bendable because the conditioner contacts so much less of the whole of the hair.
Plasticizers in hair work like lotion or cream on dry skin – soften, seal in moisture, or attract moisture. But they also add an element of pliability and flexibility (plasticity) that the hair may not have on its own. Like oiling leather or polishing a dry leather shoe, something inflexible becomes flexible, softer and glossier with the addition of a plasticizer (oil or shoe polish).
©Science-y Hair Blog 2013
So if you have ever used a leave-in conditioner, smoothed coconut oil into your hair, left in a lot of conditioner – and had your hair become softer, springier, better defined as a result – you can chalk that up to the increase in plasticity.
And if you want your hair to have more pliability, you need plenty of oil or conditioner – not only to act as an occlusive (prevent moisture loss because hair + water = flexibility), but also to help your hair stay soft and to align itself with its neighbors which increases shine and wave/curl definition.
If your hair has kinking in it (this occurs in wavy-haired people as well as curly-haired people, though it is most commonly thought of in hair with very tight curls), the added plasticity of oils and conditioners also helps prevent breakage. Each little bend and twist of the fiber (kink) can be a point of weakness in the fiber. The more abrupt a directional change, the weaker that spot is. Kinky hairs softened by plasticizers bend more readily – instead of breaking.
©Science-y Hair Blog 2013
Here’s a final thought. If you have fine hair, which is dry or porous or damaged, it may act like wider hairs and need more plasticity too, but fine-haired people can usually get away with much less.
A final note: Usually you can tell if you have coarse hairs. They feel solid between your fingers. You can see them easily when held up against a contrasting background. Sometimes coarse hairs do not bend easily. But I have seen coarse hair that pretended to be fine hair! Some coarse hair is quite pliable and bendable naturally. Especially when hair is light-colored or not thick (densely packed) on your head or it is soft - it may not seem coarse when it actually is. It is only a myth that all coarse hair is rigid or feels wiry.
A final note: Usually you can tell if you have coarse hairs. They feel solid between your fingers. You can see them easily when held up against a contrasting background. Sometimes coarse hairs do not bend easily. But I have seen coarse hair that pretended to be fine hair! Some coarse hair is quite pliable and bendable naturally. Especially when hair is light-colored or not thick (densely packed) on your head or it is soft - it may not seem coarse when it actually is. It is only a myth that all coarse hair is rigid or feels wiry.
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