Fun DIY Bath Bombs Shaped Like a Birthday Cake

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Birthday Cake Bath Bomb Recipe

This birthday cake bath bomb recipe is easy to make and is a great party favor. Let’s learn how to color them and make them in a birthday cake shaped mold.

When I was asked to bring my products to a local Fairy Festival, I knew I needed to come up with something unique. In the past, I’ve sold fairy soaps, galaxy soaps that shimmer and glitter, bath salts that are full of color, and spray-on shimmer scent with essential oils.

But I needed something new.

I was looking through my molds and it hit me when I saw a cake mold: a birthday cake bath bomb recipe!

Basic Bath Bomb Recipe

Bath bombs are very easy to make. The basic recipe is one part citric acid to two parts baking soda.

Tip: you should also check out my fizzing and spinning bath bomb recipe!

Some recipes call for cornstarch or additional kaolin clay to make it harder, but I’ve found that the basic recipe is all you really need. Citric acid is often thought of as too harsh, but the baking soda helps to neutralize it enough so it doesn’t irritate skin.

Some recipes also call for oil or melted shea or cocoa butter. If you add any of these, keep it light so you don’t slip and slide in the tub.

You can also add dried, powdered herbs for color. Natural food coloring also works well. Added colors just make birthday cake bath bombs look so much more fun.

Water makes up a very small portion of the birthday cake bath bomb ingredients, but it’s important to use the right kind. I always use distilled or filtered water since tap water can contain contaminants or chemicals.

Finding the Right Birthday Cake Mold

For this project, you’ll need a silicone cake mold. I found one that has 8 separate sections which works great. You can use a mold that makes the whole cake, but you’ll need to create sections. To do this, you can use pieces of cardboard wrapped in plastic wrap. Whole cake molds are available in 8 or 9-inch sizes.

Silicone cake molds are very flexible, so be sure to place yours on a stable surface like a cutting board or cookie sheet. This makes it easy to move the mold to a new location for drying. You don’t need to grease the mold, but be sure it’s thoroughly dry before using.

Birthday Cake Bath Bomb Recipe

Birthday Cake Bath Bomb Recipe 2

Ingredients & Supplies


1. Mix the citric acid and baking soda in a glass or stainless steel bowl. If there are any clumps, sift them out or mash them well. Add the light oil and mix well. I wear gloves and mix it well with my hands. This seems to work better than with a spoon.

2. Divide birthday cake bath bomb mixture into 3 bowls (one for each color). Add a different color to each bowl. Beetroot powder will result in a nice pink color, turmeric will lend a yellow hue, cocoa powder will look like a chocolate layer, and powdered chlorophyll will give a green to blue-green color. You can also use liquid food colors to achieve any color you like. (If liquid colors are added directly to powdered mixture they are harder to blend, but it’s easier to get the exact color you want.)

3. You can add 5-6 drops of essential oil to each mix. Choose a different oil for each mix or use the same one on each layer. Mix well with your hands again.

4. Fill a spray bottle with water. Spritz powdered mixture with water once and mix well with your hands. You may only need to spray 2 or 3 times. Slowly spritz the powder mixture while mixing with your hands after each spritz. You do not want too much fizzing to occur during this stage or the finished product will not fizz much in the bath.

5. Use your hands to check the consistency of the mixture. As soon as the mixture holds its form when squeezed in your hand, it is ready to be packed into molds. (See photo below.)


The mixture will still look very powdery when it is ready, but over-watering will cause the birthday cake bath bombs to puff up and swell in the mold.

Making Bath Bombs

6. I start with one color, mix it well, then press it into the bottom of each cavity. Keep in mind that when you are done, the bottom will become the top, because you’ll be turning it over.

7. Mix the other two colors one at a time, then pressing each into the mold. You can fill the mold entirely, or only part way. Allow birthday cake bath bomb recipe to dry overnight, or longer if they are very large.

If Your Bath Bombs Swell

The first time I made these, I got a bit too much water. I packed in my three layers and filled molds to the top. Then it started to puff up and swell, so I pressed it back down periodically for nearly an hour before it settled down. The next day, I took the cake slices out of the mold. They looked great, except for a few cracks and a dent in the bottom of one. This is where creativity comes in. I melted some white glycerin (melt and pour) soap base and drizzled it over the top. It worked great! No one could tell that I made any mistakes. I topped the soap with a few pre-made cake decorations, like butterflies and flowers. Needless to say, they were a big hit!

Birthday Cake Bath Bomb Recipe 3

To Use

To use the cake slices, just drop one into a tub of warm water. Watch it foam and fizz as it gently colors the water. NOTE: If the colors are very dark they could stain light-colored linens.

Be careful getting in and out of the tub in case the oils have made it slippery. Clean the tub well when you’re done.

Birthday Cake Bath Bomb Recipe Notes

  • You can use all sorts of things for colors, such as other herbs and spices or powdered pigments or micas. In most cases, you’ll want to keep the colors very light. Pigments can stain (although I have never had any staining), certain spices can be harsh on the body, and micas can stick to things.
  • There are also naturally based liquid food colors that could be used. I would use a few spray bottles and mix some color into each one. This will keep the color very light. You can also add the liquid food colors directly to your powdered mixture for a darker color, but it will take lots of mixing to disperse the color.
  • If you use cocoa or shea butter, melt it before adding it to the powder. This will help it combine better.


About Debra Maslowski

Debra is a master gardener, a certified herbalist, a natural living instructor, and more. She taught Matt and Betsy how to make soap so they decided to bring her on as a staff writer! Debra recently started an organic herb farm in the mountains of Western North Carolina. You can even purchase her handmade products on Amazon!

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  1. Lynne says

    Lovely recipe, and they turned out really well….apart from the fact that my top layer is v.e.r.y. crumbly and uneven. Any suggestions please? ?

    • Debra Maslowski says

      There are a couple of things you can do, Lynne. First, make sure you have enough moisture, but not too much. It should hold together like damp sand, but still be a little crumbly. Then, you can also pack the mold more. Don’t be afraid to really pack the mixture in there. It’s less likely to be crumbly if it’s packed in well. And you can use something with an even edge, like a glass bottom, to control how even it is. Hope this helps!

  2. Lori A. says

    This is great information. I have only made them once, and I too added to much water and my puffed up also. Live and learn I guess.

  3. Karen says

    This is awesome. I just dropped a ton of money at Lush so I wish I would have seen this before! 😉
    Thank you for sharing this.