How to make a bath bomb

Create your own bath bombs at home with this step by step guide from the Ri and L’Oréal UK & Ireland, the headline partners of Science Zones at Butlin's.


Bath bombs fizz and break up when dropped into water, releasing all the smells and colour.The fizzing is caused by the ingredients in the bath bomb reacting together in the bath waterto produce a harmless gas – carbon dioxide.

The main ingredients are a weak acid – citric acid – and a weak alkali – sodium bicarbonate.When they react together, they ‘neutralise’, meaning that they create a product that isneither acid nor alkali, just like water!

What you'll need

Ingredients for one bath bomb:

  • 40g Sodium bicarbonate powder(baking soda)
  • 20g Citric Acid powder
  • Liquid colour (check that the colour does not stain your skin before using)
  • Fragrance or essential oil
  • Witch hazel (can be substituted with water)


  • Mixing bowl
  • Whisk
  • Scales
  • Shape mould
  • Tile or similar surface
  • Baking paper
  • Spray bottle for witch hazel/water


  1. Weigh out 40g of Sodium Bicarbonate into a mixing bowl.
  2. Add 20g of Citric Acid to your bowl.
  3. Use the whisk to gently mix and press out the lumps. (You want a fine powder consistency.)
  4. Add roughly four drops of a liquid colour (or two drops of two different colours!) and mix well. (If you add too much liquid, the bath bomb will start to fizz.)
  5. Add three drops of the essential oil and mix well. If you are using any of the optional ingredients then add these now.
  6. Add three sprays of witch hazel to the mixture and mix well with the whisk or your hand. If you use water you want to use as small an amount as possible as the neutralisation reaction will start. (You want the mixture to clump when compressed. A consistency of slightly wet sandis ideal.)
  7. Scoop small handfuls of mixture into the mould and pack tightly with your fingers or thumbs. Keep adding and packing mixture until the mixture is level with the top of the mould.
  8. Cover a surface with baking paper and turn out the bath bomb. Turn the bath bomb out as close to the surface as possible to avoid breakages. Lift the mould to leave the bath bomb behind on the tile. (If the mixture is too dry or not packed in enough, the bath bomb maycrumble. Tip back in the bowl and try again, but repeatedly packing thepowder makes it increasingly difficult to create a solid bath bomb.)
  9. Leave bath bomb for around one hour to dry and solidify. (The longer the bath bomb is left, the more solid it will be. This canbe sped up by warming up to 50°C.)

Feel free to play around with your bath bombs and experiment withcolours, smells and other ingredients like glitter or dried flowers (thoughdo consider the clean up after your bath!).The recipe can be scaled up, just make sure you have a 2:1 ratio of sodiumbicarbonate to citric acid.