The science of curly hair

Beyonce Knowles.

Beyonce Knowles. Photo: Johnny Nunez

Have you ever wondered why you rarely see curly haired cartoon characters? (Merida in 2012’s Brave is one of the few exceptions and Pixar had to completely redesign their CG hair simulator to achieve that.) The answer probably wouldn’t surprise any lady in possession of a spirally mop of hair – curls are complicated.

A rather fascinating recent joint research paper from MIT and the Université Pierre et Marie Curie has come up with the first ever detailed 3D model of a strand of curly hair. To put that achievement in perspective mathematician Leonhard Euler came up with an algorithm for straight hair in 1744. The research wasn’t initially focused on hair as co-author of the paper Pedro Reis had been looking at the curvature of thin flexible rods for his work as an assistant professor in MIT’s Department of Civil and Environmental Engineering and Department of Mechanical Engineering. But he realised his findings would apply equally well to the modelling of hair and got in touch with the Université Pierre et Marie Curie’s Basile Audoly who had developed a theory to explain the 2-D shape of human hair. 

So what did they find out? They identified the main parameters for curly hair as curvature (relating to the ratio of curvature and length) and weight (relating to the ratio of weight and stiffness). Because of the interplay of these factors a curl can change ‘from 2-D to 3-D local helix to 3-D global helix, and back again’. The paper also looked at how there is more weight at the top of the strand than at the bottom due to gravity and how this means ‘if the weight on a hair is too great for its innate curliness, the curl will fail and become either straight or helical, depending on the strand’s length and stiffness’.   


Now we don’t want to jump to conclusions, but this does rather seem to explain why bad hair days seem much more prevalent amongst those of us without pin straight hair and why it can be so demanding to try to wrangle ‘perfect’ curls. So to any curly haired women out there, next time your hair is being ‘demanding’, don’t blame your styling skills, blame physics. After all you’re a complicated woman, so why not be proud of your equally complicated hair?