How do you choose the right oils for the soap you want to make?

Before selecting your oils, you must first understand what happens during the production of a natural soap. In the cold-process saponification method, oils and butters react with a lye (sodium hydroxide) solution. This reaction transforms the oils into soap and glycerin.

Oils + lye → soap + glycerin

Once the reaction is complete, the original oils no longer exist in their initial form. Nevertheless, the choice of oils remains crucial, as they directly influence the finished soap. The unique composition of each oil dictates the final properties of your soap, such as its hardness, its lathering ability, and its gentleness on the skin. This is why a recipe consisting solely of coconut oil will yield a different result than one composed primarily of olive oil.

Each oil brings its own characteristics

Oils are composed of various fatty acids. Each oil has a distinct profile that contributes to the properties of the finished soap. Some oils primarily enhance hardness and cleansing power, while others are particularly useful for improving lather. It should also be kept in mind that a single oil can serve multiple functions simultaneously. Moreover, the fats used in soapmaking can be categorized according to their primary role.

Base oils and butters

These fats can make up a significant portion of the recipe. Olive oil, for example, is highly valued in soapmaking for creating gentle formulas. It produces a rather creamy lather and helps result in a pleasant, mild soap, provided it has undergone a sufficiently long curing period.

Hardening oils and butters

These fats are used to add hardness to soap and, depending on their profile, to enhance its cleansing power. Coconut oil is known for firming the soap and producing an abundant lather with generous bubbles. However, caution is advised: an excessive amount of cleansing oils can result in a soap that is too harsh or drying for certain skin types.

Complementary oils

Some oils are most effective when used in small to medium quantities as a supplement to a formula. Castor oil is a prime example; it is known for helping to stabilize and enhance lather, specifically the bubbles created by other oils. It should be used sparingly, as too high a proportion can soften the soap and alter its texture. If a soap recipe contains an excessive percentage of castor oil, the resulting bar will lack sufficient firmness and will melt away rapidly in the shower. 

Examples of oil percentages based on the desired effect

Soap for sensitive skin: 70% olive, 20% shea butter, 10% sweet almond (gentle, low-lathering soap; ideal for reactive skin).

Lathering soap: 55% olive, 25% coconut, 10% shea butter, 10% castor oil (produces a rich, dense lather; perfect for daily use).

Nourishing soap: 50% olive, 20% coconut, 20% shea butter, 10% macadamia (highly protective against dryness).

What percentage should be used?

There is no universal ratio that applies to all recipes. To begin formulating, you can use the suggested ranges to create a simple, balanced recipe.

These percentages serve as formulation guidelines rather than absolute rules. Some oils can be used at much higher percentages, while others are better suited to smaller amounts. You should take into account the properties of each oil and the total quantity used in your recipe.

How do you balance a soap recipe?

A good recipe is not just a random collection of various beneficial oils; it requires finding a balance between different properties. When selecting oils for a soap, the goal is not to hunt for the "perfect" oil, but rather to develop an understanding of the process:

1. What kind of soap do I want to create?

Gentle? Foaming? Hard? Creamy?

2. Which oil can provide the desired property?

3. Which other oil can help balance that property?

Ultimately, a good recipe is, above all, one that is balanced and logical. You can start with a few simple oils, learn to understand them, and then gradually evolve your formulations.