Too much air caused Ivory soap to float. It was originally an error in production.
In 1878, Harley Procter and cousin James Gamble decided to create for their company a white soap that would rival the popular castile soaps of their competitors.
The product was successful. Then, in 1879, a worker mistakenly allowed the soap solution to be over-mixed.
The new version of the soap was an immediate success because it bobbed to the surface of the water.