Bath Bomb Ingredients: Functions and Usage Rates
I often got asked "What makes a bath bomb fizz"?"Why do we need to add oil?", "What is Cream of Tartar for?" etc, etc, etc. If you want to make bath bombs successfully you need to know what the function of your ingredient is. If you want to change your recipe and not end up with a big pile of mess you need to know what the function of your ingredient is. If you want to make your bath bombs foamier or more moisturizing or to slow down the fizz and make them last longer you need to know what the function of your ingredient is.
So in this post, we are going to talk about the most common bath bomb ingredients, their recommended usage rates, and their function. The usage rates that I mention in the table are approximate and are there just to give you my perspective. You're going to see other bath bomb creators using these ingredients at different % and it's totally fine. It doesn't mean that they're wrong. For example, if they decide to use only 4 ingredients in their bath bombs then naturally their baking soda and citric acid % are going to be higher than recommended by me. Just keep that in mind.
Name
INCI
Usage Rate (Approximately)≈
Function
Notes
Baking Soda
SODIUM BICARBONATE
56%
creates fizzy reaction when used with citric acid
Citric Acid
Citric Acid
28%
creates fizzy reaction when used with baking soda
Cornstarch
Zea Mays (Corn) Starch
4-15%
slows down the fizzing reaction
when used in large quantities might cause powdery bath bombs
Salt
depends on the type of salt you're using
2-10%
slows down the fizzing reaction
Epsom Salts and Ded Sea salts are humectants and they draw moisture into bath bombs. It's not a bad thing if you live in a dry climate but it could be an issue if the humidity in your area is high.
Cream of Tartar
Potassium Bitartrate
2-8%
acts as a hardener
you could substitute it for Kaolin Clay
Kaolin Clay
Kaolin
2-5%
acts as a hardener
when used in large quantities might cause bath bombs to crack
Milk Powder
depends on the type of milk you're using
2-8%
creates foam
you can choose from a variety of milk powder: Coconut, Goat, Regular, Buttermilk etc)
SLSA
Sodium Lauryl Sulfoacetate
0.5-5%
creates bubbles, slows down the fizz, makes your bath bombs last longer
it's a gentle surfactant.
SCI
SODIUM COCOYL ISETHIONATE
0.5-5%
creates bubbles, slows down the fizz, makes your bath bombs last longer
it's a gentle, very mild surfactant aka Baby Foam. I also use it for making my
from scratch.
Natrasorb
Tapioca Starch
1-4%
anchors your scent, helps to disperse your fragrance oils and essential oils, provides a soft feel to the water
It's not the same as Tapioca starch that you buy in a food store.
You typically need to mix Natrasorb Bath with your fragrance oils or essential oil in a 1:1 ratio
Colloidal Oatmeal
Avena Sativa (
Oat
) Kernel Flour
1-2%
soothes the skin
I like to add this powder to my Oatmeal and Honey Bath bombs
Oils and Butter
depends on the type of oil or butter you're using
1-3%
moisturizes the skin, binds the mixture
it's recommended to use a lightweight oil like sunflower, safflower, grapeseed, sweet almond, apricot kernel, etc for your bath bomb. But you could experiment and test different oils to see what is the best option for you.
Polysorbate 80
Polysorbate 80
0.5-1.5%
disperses oils and oil-soluble or insoluble
and glitter
use it in a 2:1 ratio with your oils (2 parts oil and 1 part Polysorbate 80)
Polysorbate 20
Polysorbate 20
1-3%
disperses oils and oil-soluble or insoluble
and glitter
it's weaker than Poly 80 so you should use it at a 1:1 ratio. More often than not it used for lightweight oils or fragrances.
Colorants
depends on the type of colorant you're using
0.01-0.2%
colors your bath bombs, foam, water depending on the
you're using
the most common colorants used in bath bombs are water-soluble dyes, lakes, and micas. Make sure your dyes and lakes are FDA certified for use in cosmetics if you are planning on selling your bath fizzies.
Fragrance oils
Parfum
1-2% (depends on the recommended usage rates provided by your supplier )
makes your bath bombs smell nice
Essential oils
depends on the type of essential oil you're using
depends on the type of essential oil you're using
makes your bath bombs smell nice and are known to have a therapeutic effect
Binder
depends on the type of binder you're using
depend on the humidity levels
binds your mixture together
Your choices are water, witch hazel, rubbing alcohol. When you use water then make sure to add it very slowly and mix fast to avoid activation of your bath bomb mixture. I need about 1-2ml of water per 500g batch.
Let's take a look at one of my recipes. As you can see I included a surfactant (SCI) at a very low % so we are still going to get a pretty good fizzing reaction with nice, creamy foam. Do you want more bubbles? Add SLSA. Would you like your bath bombs to be very moisturizing? Include some kind of butter in your formulations. Your bath bombs are dry, they are cracking and you notice that the humidity inside your house is pretty low? You could solve this issue by adding more oil, using water as your binder, and reducing cornstarch.
I hope this information is going to help you formulate your own recipes, tweak mines, and understand why we add a certain ingredient to a concoction.
If you're a beginner then here's the list of suppliers and a basic bath bomb recipe with instructions.
If you're interested in how to convert % into grams and why I use % for my recipes then this post is going to be extremely useful.
If you're struggling with keeping track of your supplies, recipes, notes, etc then feel free to use my Inventory and Sales Tracking Base (it's free of charge).
If you’re interested in making bath bombs check out these products :