Bath bombs are simply mixtures of dry ingredients that are tightly packed together, usually into a hard-sphere. They tend to effervesce the as soon as they come into contact with water. So, the moment you drop a bath bomb in a tub full of water, it will spin, fizz, and explode, bursting into a kaleidoscope of colors and a range of incredible smells. For most people, the best part about using a bath bomb is watching it spin and whirl in the water, and then suddenly blowing up and revealing a spectacle of color, fragrance and popping fizz.