Every bath bomb starts with the same core ingredients: citric acid and sodium bicarbonate (baking soda). When these two hit the water, the fizzing reaction begins. The standard starting ratio is 2 parts baking soda to 1 part citric acid. Bath bombs serve a similar purpose as soaks and scrubs, but are pressed together to form a solid product that fizzes in the tub.
Bramble Berry's bath bomb projects library covers dozens of recipes with step-by-step instructions and videos. Whether you are making your first round bomb or experimenting with layered colors and embeds, there is a project to guide you through it.
What Goes Into a Bath Bomb
- Baking soda and citric acid: These are the base of every recipe. Baking soda provides the bulk and helps the bomb hold its shape. Citric acid drives the fizz. Use a 2:1 ratio by weight as your starting point and adjust from there.
- Butters and oils: These bind the dry ingredients together and add a silky feel to the water. Shea butter and cocoa butter are popular choices because they harden the finished bomb. Liquid oils work well too, but use them sparingly. Too much oil prevents the bomb from setting firm.
- Colorants: Micas are the easiest starting point. Add them directly to your dry ingredients, starting at about 1/8 teaspoon per batch. Because micas are oil-based, pair them with polysorbate 80 to prevent color from clinging to the tub. Without it, you could see a ring where the color settled. Liquid dyes are water-soluble and disperse on their own without that extra step.
- Fragrance and essential oils: Both work well in bath bombs. Add them to your oils before mixing into the dry ingredients to help disperse evenly throughout the batch.
- Additives: This is where makers unleash their creativity! Botanicals, clays, and salts can add beautiful touches to any recipe. Polysorbate 20 or 80 is used to bind oil and water together and acts as an emulsifier, so you don't get 'oily tub' when using nourishing and conditioning oils in your bath fizzy.
Tips for Getting Clean Releases From Bath Bomb Molds
Silicone and metal molds both work great. Silicone releases easily and is forgiving for beginners. Metal molds produce sharper edges and a denser pack. If your bombs tend to stick, add a few drops of cyclomethicone to the mold halves, swirl it around to coat.
Once packed, leave bombs in the mold for at least 24 hours before unmolding. Then set them on a towel or foam surface and let them cure for another 24 to 48 hours before wrapping. Humidity is the most common reason bombs crack or expand after unmolding. If you live somewhere humid, a small dehumidifier in your workspace makes a significant difference.
For packaging, you can leave finished bombs in the mold or use shrink wrap soap bands sealed with a heat gun.
Check out our bath bomb kits if you want pre-measured ingredients and printed instructions.
Why did my bath bomb look amazing when I tested it in a bowl, but barely fizzled in the full tub?
This is one of the most common issues for new makers. A bath bomb will react the same way in a small bowl as it does in a full tub, but in a larger volume of water, the results can feel more diluted once it dissolves.
Bramble Berry bath bomb recipes are designed to work well in a standard tub size and produce consistent results. If you are using your own recipe and running into this issue, there are a few adjustments worth trying. Shift the baking soda to citric acid ratio from 2:1 to 1.5:1, or add cream of tartar at around 5 to 10 percent of your citric acid amount. Both citric acid and cream of tartar can increase fizz. Reducing oils and butters can help, too, since too much fat can slow the reaction. You can also try packing the mold less tightly so the bomb dissolves faster and releases a stronger fizzle.
Storing in a humid environment can also affect performance over time, since moisture can reduce fizz before use.
Why did my bath bombs crack right down the middle after unmolding?
The crack usually forms at the seam where the two mold halves meet, and the most common cause is too much moisture in the mix. Switch from water to witch hazel as your binding liquid, and reduce the amount you add until the mixture just barely clumps when you squeeze a handful. Unmolding too early is another common culprit. Wait at least 24 hours, and before pulling them out, gently press on the back of the mold. If the bomb feels soft or gives under pressure, leave it longer. It should feel completely firm before you attempt to release it.
Do I need polysorbate 80, or can I skip it?
If you use micas or oil-based colorants and you like your tub to stay fairly clean, you need polysorbate 80. Without it, the oil-based color will float on the water surface and leave a residue on the tub. Water-soluble liquid dyes disperse on their own and do not require it (though, like any color, if overused, they will dye water and potentially stain tubs and bodies).