Why does some wavy hair curl, and others does not? Some wavy hair will curl with certain styling products, with humidity – just plain unpredictably on some days and not on others. In this post the story was about how fine hair often does not have the structural support to maintain a wave of curl if there is weight on it from the sides or weight from length (or water or styling products). Many people with wavy hair, especially wavy hair that does not wave and curl consistently have fine hair and that explains much wavy-haired frustration.©Science-y Hair Blog 2013
But this doesn’t explain how people who have average-width or wide (coarse) hair can have loose waves too. Or how wavy hair can be fairly curly. Imagine driving a car or a bicycle. You turn the steering wheel or handlebars just a little. You will begin to turn in a large circle – you may run out of space to complete your turn. If you turn the wheel more sharply, you will make a sharper turn and go around in a tighter circle. That’s pretty much the explanation - but I've got a visual aid below.
©Science-y Hair Blog 2013
In this post, we dug into the biology of how hair curves. You have these variables:
1) A large variation in the way various proteins are arranged on different sides of the hair means a smaller curl circumference (bouncy curls), but it can also mean a curl that is more robust and doesn't pull out easily vs. a curl that drops out without a lot of styling products. And a smaller variation in the way these various proteins are arranged means a larger curl circumference (undulating waves). The intensity of the curl as determined by these variables will determine how well your hair holds a curl. Generally, tighter curls resist gravity and weight better than looser ones because the curve of the fiber is stronger.
2) The width or diameter of the fiber determines how structurally well-supported it is and how well it can withstand forces from the outside (other hairs, gravity) – fine hair has more difficulty maintaining the spring in its curls than does wider hair.
3) A hair has to wave about 3 times in order to form a curl. So if your wavy hair has the crests of each wave 3 or 4 inches apart, you need plenty of length to get your hair to make any sort of spiraling curl, or even for the waves to make themselves quite clear.
In this attempt at an illustration (I make no apologies, I am not a graphic designer), you see in dark blue a loose-ish curl circumference. Let’s say the crests of the waves are 2 inches (about 5 cm) apart, which is quite wavy hair. The circle then is probably about 1 inch (2.54 cm) in diameter – but gravity stretches that circle into a spiral. The arrows indicate where each wave appears so that you can see where a wave’s crests and troughs fits into the context of a curl.
Below this in green is a much larger circle/curl. Let’s say the crests of the waves are about 3.5 inches apart (9 cm) and the circle outlining the curl is around 2 inches in diameter. These are loose, glamorous, “beach” waves. Because of the large area circumscribed by the curl, when exposed to gravity, it will be pulled into a loose wave or very gentle spiral. The twist on the hair may not be readily discernable under some conditions. If you give hair like this enough length and relieve it of its weight by having layers, or using a diffuser (on low temperature) to press hair towards your head while you dry, and use styling products such as hair gel to help the hairs hold together while they dry, you will see some twists and turns.
©Science-y Hair Blog 2013
Curls and waves are really the same thing, but with a different “turn radius." I know that should be "radii" but it just felt way too pedantic to put into a sentence. Not that using the word "pedantic" isn't also a bit priggish. At least by USA standards.
Waves are curls, it’s a matter of physics.