We hand press our bath bombs.  We add avocado oil and hemp oil for skin loving properties and kaolin clay for a silky feeling. 
Our essential oil bombs are all natural containing powdered goat's milk for some foaming action, natural clays and herbs for a tinge of color, and avocado and hemp oils for skin benefits.
For those that like a little bath art, our fragrance oil bombs contain FD&C Lakes and Dyes for beautiful colored foam and water.  The SLSA (Sodium Lauryl Sulfoacetate) provides the foaming action.  It is derived from coconut and palm oils and is skin safe/skin friendly.