Saturday, March 17, 2012

More Wavy Physics

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. 


  1. I love this site! Your info is awesome, I thoroughly enjoy learning about my hair :)

  2. Why thank you, I'm so pleased somebody has found something useful here!

  3. That is very interesting. Thank you for taking the time to write and post this! :)

  4. Do you know of any products that encourage waves? I started using Dr. Bronner's shikakai citrus rinse and my waves got more intense. But not more curly. Gel will make my hair more curly. Do you know why the shikakai rinse made my waves more intense? There are several ingredients in the product, but I was assuming it was the shikakai. What do you think? Also, are there other ingredients that will do the same thing? I like the effect and want to make my own conditioner!

  5. Charlotte,
    The Dr. Bronner's rinse you mentioned appears to be liquid soap from the ingredients listed on their website. Soaps tend to leave some residue on hair - soap residue (largely oils, maybe the shikaki) if you have soft water and oils plus minerals if you have hard water. Both can intensify waves because it creates a little friction that prevents waves from falling out.

    Usually soap bars are much too alkaline for hair (pH is usually 8 and I usually see hair swell up in soap bar lather). Best used only occasionally.

    Ingredients that can boost curl include protein (unless your hair is very coarse), "curl enhancers" which are usually jelly-like in texture and based on plant gels like aloe, flax, marshmallow root, pectin or seaweed extract.

    If you're looking for the slight friction that kept your waves more intense from the Dr. Bronner's product, look for ingredients like magnesium sulfate (epsom salt - but use it in moderation, it can be drying), shea butter (also use in moderation because it tends to build up), xanthan gum, henna (for example, "neutral henna" in conditioners), starches, stearamidopropyl dimethylamine in conditioners or styling products. Any of these may give your hair a little more friction or traction to make your waves more intense.

  6. This is the product I was talking about:

    I think it's mostly lemon juice and shikakai. But there is some potassium hydroxide converted to a fatty acid. Is that a soap?

    I tried some plant gel (slippery elm) and when I put too much in it made my hair really flat! Even in a rinse out conditioner! I was surprised, because I thought because it was water soluble it wouldn't do anything in a rinse out product. I'm also surprised it made my hair flat if you say plant gels can enhance curls. That's weird!

    What kind of starches enhance curl or wave? Thank you for all your expertise!

    1. The ingredient list for the Dr. Bronner's product looks like a liquid soap to me. If you want to make your own conditioner, look up suppliers of cosmetics ingredients (lotioncrafter,, ingredientstodiefor). They sell ingredients and provide sample product formulas. Also check out for "how to" on conditioners. What we're usually looking for in a conditioner is something that makes hair feel soft and helps remove tangles/provides lubrication. Conditioning ingredients (cationic conditioners) are very good at doing that.

      Slippery elm is a plant gel, but some of those do leave a dull or heavy residue that needs to be removed with shampoo.

      Plant gels are good for enhancing curls when they are used as a hair gel or are included as an ingredient in a conditioner. Too much of a good thing can often give us flat hair. Flaxseed gel enhances curls because it is thick and works as a setting lotion and helps keep hair hydrated. Aloe helps enhance curls because it improves hair hydration. Every plant gel has different qualities and different applications it is best suited for.

      If you're wanting to make a very "natural" homemade conditioner without special-order ingredients, you might try using my curl boosting jelly as a base (double the water or cut the xanthan gum in half so it's less thick) and add 1/8 teaspoon or more of an oil you like - the amount depends on how your hair feels. The oil is meant to add lubrication and softness.

      Tapioca starch is good to use in products. It needs to be heated to thicken. Cornstarch works to thicken and make a "gel" but it tends to separate and get watery.

  7. Do aloe, flax, marshmallow root, pectin and seaweed extract enhance curls in a rinse out product? And is flax the best at enhancing curls?

    What are examples of starches that increase friction and therefore waves? Are xanthum gum, tapioca starch and cornstarch good examples? And do they produce different kinds of waves from the plant gels above?

    1. Aloe is good in conditioners and marshmallow root can be good in cleansers and conditioners for lubrication. Seaweed extract, flax gels, marshmallow root and pectin are good in styling or leave-on products because they form films to provide a little hold as well as hydrate hair. Some are thicker and more stretchy and therefore product better hold.

      Starches that enhance friction include cornstarch and tapioca starch. Xanthan gum is not technically a starch and it produces a different feeling sort of gel.

      Flax gels and xanthan gum gels tend to be a little heavier than starch gels. But they also tend to hold together better when hair is dry. The gel is just the base of a styling product, much depends on what else is added. Starches can have some hold, and may provide a little curl enhancement on their own, but they're often at their best when combined with other gelling or thickening ingredients.

    2. Would starches work to enhance curls in a rinse out product?