Polysorbate 80
It is a nonionic surfactant used to aid the mixing of oils in water.
In simple terms it is to ensure oils used in the bath bomb are distributed through the bath and do not congregate on the surface. It also aids in the distribution of colorants and thus reduces bath staining.
We at No Probllama use plant based polysorbate 80 and this is vegan and also not palm derived.