Here’s an easy, children’s recipe on how to make bath bombs. Follow the method below and find out how we have adapted the recipe to make it simpler for children to do. These bath bombs are rainbow coloured too! We also explain the science behind why bath bombs fizz.

Following our Rainbow Bath Bombs workshops in Devon during May half term, I wanted to share with you the *new* recipe we were using because it is slightly different from many recipes out there. The main ingredients in bath bombs are powder based (more below) and you need to add a liquid, often water, to bind these powders together to make them into a bath bomb. However you need to add just the right amount of the water to ensure the powders stick together but do not start reacting – this was the tricky bit for children previously, but our new recipe works well.


  • 4 cups
  • Stirring sticks/spoons
  • Sodium bicarbonate (baking soda)
  • Citric acid (powder or granules)
  • Mineral salts or Epsom salts
  • Red, yellow & blue food or cosmetic colouring
  • Essential oil (to add scent) – your own choice
  • Oil  –  any kind will do, olive oil, coconut oil, almond oil…even sunflower oil if you have nothing else!
  • Pipettes for measuring the oil
  • Mould or other small container to hold the bath bomb whilst it dries (we use paper ramekins)
easy childrens bath bomb recipe (1)

Some of the ingredients for the rainbow bath bombs


1)   Put the following ingredients into one of the cups and mix them together really well together.

3 heaped dessertspoons of sodium bicarbonate
2 heaped dessertspoons of citric acid
1 heaped dessertspoon of mineral salt

2)  Next, add 3ml of oil, and mix it in really, really well. Add more oil, 1 ml at a time until the powders clump together and resemble damp sand.

…Now, make this powdered mixture into rainbow colours…

4)  Separate the mixture equally between 3 cups.
5)  Add 2 drops of red colouring to cup 1 – notice the fizzing? Stir quickly and well to blend the red into this first mixture.
6)  Repeat with the yellow and blue colouring, taking care not to add so much colouring that you can not mix away/stop the fizzing reaction (disaster!)

* You now have 3 coloured bath bomb mixtures * Horrah!

…Next, prepare the bath bomb for drying….

7)  Scoop out the red and put it into the mould/pot and push it down with you fingers until it is squashed into the bottom of the pot. Add the yellow on top, squish it down, then add the blue last, and press this down too. The colours should blend together a little to make orange and green layers thus creating a rainbow effect.
You could try and make the colour stripes vertical, or mix them altogether to create a different effect….its up to you!

8)  Allow to dry for at least 2 days until it is rock hard.

9)  Put it into an airtight bag for storage or use it straight away. When you fancy a relaxing bath, drop your bomb into the bath and watch it bubble and fizz.


lab notes


Notice we didn’t add any water to bind the powders…this is what children find tricky to get perfectly right. If you add too much water the powders will start reacting and you can’t stop it! Oil is more forgiving, it doesn’ start the reaction off easily like water, but it will eventually if you add too much.

Dry/crumbly bathbombs?

If, after the bath bomb has dried, it is crumbly, this means you did not add enough oil to bind to ingredients together. Remember it is supposed to resemble damp sand (the kind of sand that is good for making sandcastles) before you press it into the mould.

Other ingredients.

Ther are loads of other ingredients you can add, petals, biodegradable glitter, even corn flour (which make them lighter). They all have their place, but the recipe above is designed to be simple for children to follow. Experiment!

easy child friendly bath bomb recipe (3)

Try different colours & biodegradable glitters

Other colours.

Just use 1 colour if you prefer, but the rainbow effect is just soooo pretty!


There are numerous mould designs on the market, these can be quite pricey. We use paper ramekins as we make a lot of bath bombs with kids and they can take their bath bomb home it it for drying. For making bath bombs at home, any small mould will do, no need to spend a fortune, although you will want to consider that you need a mould that you can get the bath bomb out easily when it has dried.

The science bit!

There are different recipes for bath bombs but the 2 key ingredients which create the “fizz” are citric acid & sodium bicarbonate. When dry they do not react, but in water they create a bubbly chemical reaction. Here’s how it works:

Sodium Bicarbonate has the chemical formula NaHCO3 and it dissolves in water, meaning the positively charged sodium (Na+) breaks away from negatively charged bicarbonate (HCO3-). In the same water, the citric acid, C6H8O7,  also dissolves, with a single hydrogen ion (H+) separating from the rest of the molecule. So, the positively charged hydrogen from the citric acid and the negatively charged bicarbonate from the baking soda come together, and quickly undergo a series of reactions, one product of which is carbon dioxide (CO2), the gas seen making bubbles in the water, creating that lovely fizz.

If you try this activity at home you do so at your own risk. If you have as much fun as we did, feel free to share your pictures with us on Facebook.

If you liked this easy science activity, how about making fluorescent glowing liquid or check out our other science experiment blogs here.

You can also check out the workshops we have coming up in Devon, why not book on?


Happy science-ing


Chief Scientist