NaOH vs KOH: Which Lye Should You Use for Soap?
Compare sodium hydroxide and potassium hydroxide for bar soap, liquid soap, and hybrid recipes, including purity and calculation differences.
NaOH makes solid soap
Sodium hydroxide, usually written as NaOH, is the usual alkali for cold process and hot process bar soap. It produces a firm soap structure when it reacts with oils. A recipe still needs the correct amount for each oil; substituting NaOH gram for gram for another alkali is not safe.
KOH makes liquid or soft soap
Potassium hydroxide, or KOH, is used for liquid soap paste and softer soap formats. KOH has a different molecular weight and is often sold at a lower purity than NaOH, so the calculated amount is different even when the oils and superfat stay the same.
Hybrid recipes use both
Some makers combine NaOH and KOH to balance firmness and solubility. The percentage split must be applied inside the calculation, not after it. Enter the actual purity printed on each product label so the calculator can compensate correctly.
Both alkalis are caustic. Wear appropriate protective equipment, use heat-safe containers, and follow an established soap-making process.