Work out soap superfat percentage instantly with clear inputs, formula shown and shareable results.
Superfatting reduces the alkali below the amount needed for complete saponification, leaving free oil in the bar for conditioning and providing a safety margin against measurement error. Five percent is standard; 1-2% suits laundry and 8-15% suits facial and shaving bars. Lye concentration of 28-33% is typical.
Superfat
Alkali = alkali at zero superfat x (1 - superfat %)
Lye concentration
Concentration % = alkali x 100 / (alkali + water)
Soapmaking uses corrosive alkali and generates heat. Wear eye and skin protection, and cure and test the final pH before use or sale.
It guarantees the bar cannot be lye-heavy even with small weighing errors or an imprecise SAP value. A zero-superfat recipe with a 2% error becomes caustic and unusable.
Less water gives a firmer bar sooner and faster unmoulding, but a hotter, faster reaction with more risk of cracking and overheating. High water gives more working time and a softer initial bar.