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

Before selecting your oils, it is important to understand what happens during the soap-making process. During cold-process saponification, oils and butters react with a sodium hydroxide (lye) solution. This reaction primarily transforms the triglycerides found in the oils into soap and glycerin.

Oils + lye ⇒ soap + glycerin

Once saponification is complete, the original oils have been transformed; they no longer exist in their initial form. However, the choice of oils strongly influences the soap's final characteristics—such as its hardness, lather, cleansing power, and the feel it leaves on the skin. That is why a recipe made entirely of coconut oil will yield a different result than one based primarily on olive oil.

Each oil brings its own unique characteristics

Oils are composed of various fatty acids. Each oil has a distinct profile and contributes differently to the soap's properties. Some oils primarily enhance hardness and cleansing power, others add mildness, while some are particularly effective at improving lather.

It is also worth noting that a single oil can serve multiple functions. To start, the fats used in soap-making 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 instance, is highly prized for creating gentle soaps. It produces a creamy lather and results in a pleasant soap, provided it undergoes a sufficiently long curing period.

Hardening oils and butters

These fats are particularly useful for adding hardness to the soap and—depending on their profile—increasing its cleansing power. Coconut oil, in particular, is known for producing abundant lather and generous bubbles. However, be careful: an excessive amount of oils with strong cleansing properties can result in a soap that feels harsher or more drying on certain skin types.

Complementary oils

Certain oils are particularly beneficial when used in small to moderate amounts to round out a formula. Castor oil is a prime example. It is best known for helping to stabilize and enhance the lather—specifically the bubbles produced by other oils. It is generally used in moderation, as too high a proportion can make the soap softer and alter its texture.

Examples of oil percentages based on the desired effect

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

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

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

What percentage should you use?

There is no universal ratio that suits every recipe. To get started, 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 generally best used in small quantities.

You must also consider the properties of each oil and the total amount used in the recipe.

How do you balance a soap recipe?

A good recipe isn't just a random combination of various beneficial oils; it requires balancing different properties. When choosing oils for a soap, the goal isn't to find the single "perfect" oil, but rather to understand the process.

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

Gentle? Foaming? Hard? Creamy?

2. Which oil provides the desired property?

3. Which other oil can balance that property?

Ultimately, a good recipe is a balanced one.

You can start with a few simple oils, learn their roles, and then gradually evolve your formulations.