Superfatting your soap simply means adding an excess amount of oil or discounting your lye amount so you end up with an excess amount of oil. You’ll hear it both referred to as superfatting or lye discounting. This excess oil provides your soap with unsaponified oils to give your soaps moisturizing or emollient properties. This process also acts as a type of “insurance” or “buffer” making sure that your soap will not come out lye heavy. A good range for superfatting is typically 3-8%. If you go below that you could end up with lye heavy soap or soap that is generally too harsh.

If you superfat with high percentages you are left with high amounts of unsaponified oils in your soap. While soap tends to have a pretty long shelf life, oils don’t and will go rancid. So a higher superfatted soap tends to go rancid quickly. A soap calculator will have an input field for superfatting and will calculate this for you. As you can see below the lower the superfat or lye discount the higher amount of lye is used. The higher the amount of superfat or lye discount the lesser amount of lye is used leaving a higher content of unsaponifed oils.

Recipe with no lye discount
8 oz olive oil
4 oz palm oil
4 oz coconut oil
2.384 oz lye

Recipe with 5% lye discount
8 oz olive oil
4 oz palm oil
4 oz coconut oil
2.265 oz lye

Recipe with 8% lye discount
8 oz olive oil
4 oz palm oil
4 oz coconut oil
2.194 oz lye

As always, be sure to use a reliable soap calculator like thesage.com!