There really is no other oil like castor oil in soap. Castor contributes to big fluffy luxurious bubbles, unlike any other oil can. Many people also love castor in shampoo bars because of its humectant and moisturizing properties.
Castor oil should not be used at more than 10% in cold process, because it will make a soft bar if too much is used. Used at lower percentages, this oil will give your soaps a bubbly kick!