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Castor oil is a thick, clear oil that helps increase the lather in soap - a rich, creamy lather. It's also a humectant (attracts moisture to your skin) oil. Just a little will do...5% - 8% in your recipe will work wonders. Shampoo bars often use 10%-15%...but more than that and you get a soft bar of soap. Castor oil has a fatty acid makeup that's completely unique—which makes what it contributes to your soap (the rich, creamy lather) unique.

Castor oil will speed up the rate at which your soap will get to trace - so we usually leave it out of recipes that require complex swirls or designs.