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 Foaming Bath Whip 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 colorants 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 colorants 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 type of colorant 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).
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