There is no definitive answer to this question as different soap makers have different recipes and methods. However, a good rule of thumb would be to use between 5-20% castor oil in your hot process shaving soap recipe.
How Much Castor Oil Do I Put In Shaving Soap? In cold process soap, castor oil is used around 2% of the total oil weight. Using more than 10% can cause a sticky bar.
How Much Castor Oil Do I Put In Shaving Soap?
In cold process soap, castor oil is used around 2% of the total oil weight. I’ve found that using more than 10% can cause a sticky bar. A small amount of castor oil contributes to a stable and fluffy lather. 
How Much Castor Oil Do I Put In Hot Process Soap?
It is recommended that 5% to 8% of the oil is used in the soap recipe. It is known that using more than 10% makes soap stick and unattractive to use. Adding one gram of castor oil is required. 
Does Castor Oil Make A Hard Bar Of Soap?
If used in higher percentages, it can make a nice shampoo bar. It will never get to the lather of a coconut oil bar. A stable lather that is low, dense, and creamy is achieved by adding castor oil to a soap recipe. 
What Type Of Castor Oil Is Best For Soap Making?
It is clear that pure castor oil is thick. The soap has a rich and creamy texture which makes it very bubbly. The humectant in castor oil is good for our skin. The castor oil in the soap recipe will make a difference. 
What Oil Makes The Hardest Bar Of Soap?
Hard oils include coconut oil, palm kernel oil, babassu oil, and murumuru butter. Hard oils include palm oil, cocoa butter, tallow, kokum butter, illipe butter, sal butter, mango butter, and shea butter. 
What Type Of Castor Oil Is Used In Soap Making?
The rich, creamy lather in soap is produced by the thick, clear oil of cacciatore. There is a humectant in castor oil. We recommend using 5% to 8% castor oil in soap recipes. 
Frank Harmenstein is the lead editor of the grooming website Cut Throat Straight Razor, and has over 15 years of experience in the industry. He’s personally tested and reviewed over 200 different straight razors, and has written countless articles on the subject.