Stearic acid is used mostly in lotions as a thickening agent, it is usually used in conjunction with emulsifying wax for lotions from scratch, but it can also be used in CP, HP, and MP soap and candle making.
Stearic acid will add hardness to a bar of soap. It also adds a creamy and stable lather to your bar. It acts a lot like a palm oil and is an attractive alternative for those who choose to not use palm products.
In CP and HP soap 0.5%
MP soap up to 3% to help harden and reduce sweat but it will cloud soap and reduce lather
In candlemaking typically 10-12%