First, a little bit of background. My wife discovered Lush bath bombs a while ago and has been totally obsessed with them since. Some of that may have rubbed off on me too, heh. The thing is, they aren't cheap, but more importantly, I like to make things. So I learned how to make bath bombs! I figured it would be a good thing to share my experience with anyone else trying the same thing. I come from a chemistry and engineering background with no prior experience in making cosmetic stuff, so my perspective might be a bit different, too. I'll start with the basics first, and then follow up with more in depth explanations of each part. Basics: A bath bomb, at its most basic, is a mixture of both a solid, powdered acid and base. They are kept from reacting with each other because they lack a common solvent, aka water. Generally, citric acid is used as, well, the acid, and baking soda as the base. Without going into the chemistry of it right now, you need about 3 parts of citric acid to every 4 parts of baking soda by *weight*. These two components and various other additions like oils, colors, scents, moisturizers, and surfactants are bound together through various means into a solid shape. Honestly, I am no expert on perfumery (maybe someone else could post which scents they think go well in bath bombs) but I do know that it’s easy to add too much. As for oils, I have found coconut oil works very, very well for several reasons (coming soon!). If you want bubbles, I highly recommend Sodium Lauryl Sulfoacetate, or SLSA. It’s a much less aggressive surfactant than SLS, and honestly, I think it makes superior bubbles. My wife has pretty sensitive skin, and she said that she couldn’t even tell (besides the mountains of fluffy bubbles) that I had used a surfactant. You should also add some ‘filler’ material, like Epsom salts, corn starch or even your favorite bath salts. (Or all of them!) Your basic bath bomb should have around half the amount of filler as it has citric acid + baking soda. Adding more filler makes it slower, and less filler makes it faster. No filler, well, think less “relaxing bathing experience with bubbles” and more “foamy fireworks in the tub”. Adding a very small amount of water to the dry mix lets it clump up, and then all you need to do is press it firmly into a mold and let it dry. The resultant solid shape gets dropped into water, the reaction starts, and then we all stand back and watch the magic like little kids seeing our first vinegar-baking soda volcano. Fiiiiiizzzzzzyesssss! Coming up, Chemistry! Or, “How to Train your Bath Bomb” if your memories of HS chemistry are full of demonic moles with eyes made of swirling numbers and a fur coat of arcane symbols.