Sodium Bicarbonate is one of the main components in making bath bombs. When combined with citric acid, and added to water, this combination will cause the bath bombs to fizz. There is no other substitute for this. You must use this ingredient. Since it is the cheapest ingredient and most popular, you will not have an issue finding it. When you are in the store looking for it, you will find it by the food grade name: Baking Soda. While there are different grades of sodium bicarbonate, you should buy the Baking Soda grade to use for your sodium bicarbonate.
When making bath bombs, you really need to maintain some consistency with the ingredients. This will help you narrow down the potential list of problems should anything go wrong. If you change up the baking soda, the citric acid, the oils, etc. , you might not be able to figure out why something went wrong. If all ingredients stay the same, and you substitute out the Arm and Hammer with a Store Brand, and the bath bombs are different, you will immediately know why. Stick with one brand, and one size, and you will save yourself a bunch of time and headaches.
While we have tried and tested 4 different brands and even some different grades of baking soda, we have found the ARM & HAMMER Baking Soda to be the best. Arm & Hammer also sells a 50lb bag of No 1 Sodium Bicarbonate which is equally as good. Although, the No 1 grade is a bit more powdery and you will need to adjust the binding agent a bit.
Overall, we believe the Arm & Hammer baking soda is the best, easiest, and most popular brand of sodium bicarbonate you will be able to find.