Understanding Soap Oils: A Beginner’s Guide to Formulating Soap

Cold process soap may look simple, but the oils used in a recipe determine how the final bar behaves. Each oil contains a unique fatty acid profile used in soapmaking that influences lather, hardness, conditioning, and overall performance. Choosing the right oils is the foundation of every cold process soap recipe. This guide explains the most common soapmaking oils, what fatty acids they contain, and how they influence hardness, lather, conditioning, and cleansing in handmade soap.

Once you understand the role each oil plays, it becomes much easier to design your own recipes or adjust existing ones with confidence.

Note: Many traditional soap recipes rely on palm oil or animal fats such as tallow for hardness and longevity. In our formulations, we prefer to build structure using plant-based oils and butters such as shea butter, cocoa butter, and mango butter instead. While our soap recipes are primarily plant-based, some formulas may include ingredients like honey, so they are not strictly vegan. We also use fragrance blends in many of our recipes.

The Four Core Roles in a Soap Recipe

Most balanced soap formulas contain oils that serve four primary purposes: cleansing, hardness, conditioning, and lather stabilization.

Cleansing Oils

These oils produce large, bubbly lather and provide the cleansing power in soap.

• Coconut Oil
• Babassu Oil
• Palm Kernel Oil

These oils are typically used at 15–30% of a recipe. Higher amounts increase cleansing power but may make soap feel more drying.

Hardness & Structure Oils

Hard fats help create a solid bar that lasts longer in the shower while contributing a dense, creamy lather.

• Shea Butter
• Cocoa Butter
• Mango Butter
• Palm Oil
• Tallow
• Lard

These oils are commonly used at 15–30% of the formula.

Conditioning or Soft Oils

Conditioning oils make soap milder and provide a smoother skin feel.

• Olive Oil
• Rice Bran Oil
• Avocado Oil
• High Oleic Sunflower Oil

These oils often make up the largest portion of a recipe, usually 30–70%.

Lather Booster

Castor oil contains ricinoleic acid, which helps stabilize and extend the life of soap bubbles.

• Castor Oil

It is typically used at 3–8% of the total oil weight. This oil does tend to cause stickiness and a slimy feeling if you use too much, so we have found the sweet spot around 4-5% of our formulations.

The Four Things That Make a Good Bar of Soap

Every cold process soap recipe is built around four core qualities. Different oils contribute different fatty acids, which determine how the final bar performs in the shower.

Common Soap Fatty Acids and What They Do

Behind every soap recipe is a fatty acid profile. Different oils contain different fatty acids, and these determine how the finished soap behaves. Soap calculators estimate soap qualities using these fatty acid levels.

Fatty Acid	Primary Effect in Soap	Typical Range	Common Oil Sources
Lauric	Strong cleansing and big bubbly lather	20–30%	Coconut oil, babassu oil, palm kernel oil
Myristic	Supports cleansing and stable lather	5–15%	Coconut oil, palm kernel oil
Palmitic	Hardness and creamy lather	15–25%	Palm oil, cocoa butter, shea butter
Stearic	Hardness and dense creamy foam	10–20%	Shea butter, cocoa butter, tallow
Oleic	Mild conditioning and gentle cleansing	40–60%	Olive oil, rice bran oil, avocado oil
Linoleic	Conditioning but more prone to oxidation	5–15%	Sunflower oil, sweet almond oil
Linolenic	Highly conditioning but unstable in large amounts	0–2%	Flaxseed oil, hemp oil

Some Classic Beginner Soap Recipes

These simple framework recipes demonstrate how different oil combinations create different soap styles. If you're new to soapmaking ingredients, our soap ingredient glossary explains the oils, butters, clays, and additives commonly used in cold process soap.

1. Castile Style Soap (Very Mild)

Olive Oil 90–100% · Castor Oil 0–10%

This traditional soap is made primarily with olive oil and produces a very gentle, conditioning bar. The lather is soft and creamy rather than bubbly, and the soap benefits from a longer cure time (think 1 year!) to reach its best hardness.

2. Bastille Style Soap (Balanced & Mild)

Olive Oil 70% · Coconut Oil 20% · Castor Oil 10%

This version keeps olive oil as the main ingredient but adds coconut oil to improve lather and hardness. Also, this bar needs a long cure time.

3. Balanced Everyday Bar

Olive Oil 40% · Coconut Oil 25% · Palm Oil 25% · Castor Oil 10%

This is a classic balanced formula that produces a hard, long-lasting bar with both bubbly and creamy lather. For those who don't use Palm Oil, Babassu Oil is an excellent substitute.

Substituting Oils in Soap Recipes

When experimenting with recipes, oils can often be swapped with others that serve the same role in the formula.

Cleansing Oil Substitutions

• Coconut Oil → Palm Kernel Oil or Babassu Oil
• Palm Kernel Oil → Coconut Oil or Babassu Oil
• Babassu Oil → Coconut Oil or Palm Kernel Oil

Hard Fat Substitutions

• Palm Oil → Tallow or Lard
• Shea Butter → Cocoa Butter or Mango Butter
• Cocoa Butter → Kokum, Shea Butter, or Mango Butter

Conditioning Oil Substitutions

• Olive Oil → Rice Bran Oil or Avocado Oil
• Rice Bran Oil → Olive Oil or Avocado Oil
• High Oleic Sunflower Oil → Olive Oil

Always Use a Soap Calculator

Whenever you change oils or create a new formula, always run the recipe through a soap calculator to confirm the correct amount of lye needed for saponification.

Understanding how oils function in soap gives you the freedom to experiment, adjust recipes, and create bars tailored to your preferences.

Common Beginner Soap Questions

From Formulation to Finished Bars

The same principles described above guide every soap we make. Balanced botanical oils, thoughtful ingredient choices, and proper curing time are what create a gentle, long-lasting bar.