Organic Products: What are some good uses for Castile soap? Castile soap is basically a vegetable-based oil soap. This plant-based soap is a gentle cleanser with zero additives and preservatives. It is bound to be an excellent organic replacement for chemical-laden, store-bought soap. However, not just for the common household, castile soap has a lot of other uses that you can use to your advantage. How can you use castile soap in other applications? Here are a few examples.