How oils turn into soap
Soap is made when fats or oils react with lye (sodium hydroxide) in a process called saponification. The oils you choose decide most of what the finished bar feels like: how hard it is, how bubbly the lather is, how gentle it feels, and how long it lasts. No single oil does everything well, which is why most recipes use a blend.
Every oil needs a different amount of lye, so always run your exact recipe through a soap lye calculator before you make anything. Lye is caustic, so wear gloves and eye protection and follow a trusted safety guide when handling it.
Hard oils vs. soft oils
Soap makers usually sort oils into two groups.
- Hard oils and butters are solid or semi-solid at room temperature (coconut oil, palm oil, tallow, lard, shea butter, cocoa butter). They tend to contribute hardness, longevity and cleansing.
- Soft oils are liquid at room temperature (olive, sweet almond, avocado, sunflower, rice bran, canola). They tend to contribute conditioning and a creamy lather.
Many soap makers aim for a mix in which soft oils make up a large share, often somewhere around 40-70% of the recipe, with hard oils filling out the rest. Treat that as a starting point, not a rule, and adjust as you learn how your bars behave.
Core oils most recipes use
Olive oil. High in oleic acid, it makes a mild, conditioning, long-lasting bar. It is slow to thicken, which gives beginners more working time. A bar made entirely from olive oil is called Castile and generally benefits from a long cure.
Coconut oil. Rich in lauric acid, it produces big, fluffy bubbles and strong cleansing. At high percentages it can feel drying, so many recipes keep it to a moderate share, often cited as roughly 15-30%.
Castor oil. Contains ricinoleic acid, which helps build a stable, creamy lather even in small amounts. Often used at roughly 5-10%.
Palm oil, tallow or lard. These add hardness and a stable bar. Palm oil is controversial for environmental reasons (the same debate is covered in is palm wax eco-friendly), so some makers choose sustainably certified palm or an alternative. Tallow and lard are animal fats that have a long history in soap.
Shea and cocoa butter. Used for hardness and a creamy feel. They are often chosen for conditioning bars.
Specialty and budget oils
- Sweet almond oil is a light, conditioning oil that many makers find gives a comfortable working time.
- Avocado oil is valued in bars aimed at dry or sensitive skin.
- Rice bran oil is often used as an olive oil substitute, though it can thicken faster.
- Canola oil (including high oleic) is an inexpensive, widely available option.
- Sunflower and safflower oil are high in linoleic acid and feel very conditioning, but they shorten a bar’s shelf life. Use them in small amounts.
- Jojoba oil is technically a liquid wax and behaves differently from other oils. See our guide to jojoba oil in soap.
Some suppliers also sell pre-mixed soap-making oil blends, which can be a convenient way to begin.
What each oil contributes
| Oil | Typically contributes |
|---|---|
| Olive | Mildness, conditioning, a creamy lather |
| Coconut | Fluffy bubbles, cleansing, hardness |
| Castor | Lather support and stability |
| Palm / tallow / lard | Hardness and longevity |
| Shea / cocoa butter | Hardness with a creamy feel |
| Sunflower / safflower | Conditioning, shorter shelf life |
Shelf life and dreaded orange spots
Oils that are high in polyunsaturated fats go rancid faster. In soap, rancidity often shows up as dreaded orange spots (DOS) and an off smell. Fresh oils, cool dry storage, and limiting high-linoleic oils all help. Opinions differ on every contributing factor, so keep notes on your own batches.
Vegan options and animal fats
You can make good soap with plant oils alone, for example olive, coconut, castor, and shea or cocoa butter. Animal fats such as tallow and lard are still used by some makers because they produce a hard, stable bar. Which you pick is a matter of preference and values.
Building a simple blend
- Pick a soft oil as the base, often olive.
- Add a hard oil or butter for firmness.
- Add a lather-focused oil such as coconut, and a little castor.
- Enter the weights into a lye calculator and choose a superfat level. Our explainer on what superfat is in soap making walks through the choice.
- Make a small test batch before scaling up.
Once you are comfortable, you can explore additives like silk or herbal infused oils, and see how professional makers approach recipes in our piece on artisan soap.
Essential oils are not soap oils
Essential oils are used for scent, not as the fats that make soap. Some essential oils can irritate skin or are not recommended at certain levels or for certain people, so check a reputable usage guide for any essential oil before adding it, and follow the recommended maximum usage for that oil. For scent blends and how to convert them to weights, see soap scent recipes and combinations.
Frequently asked questions
What are the best oils for soapmaking? There is no single best oil. A balanced blend of a soft oil (olive), a lather oil (coconut), a hardening fat (palm, tallow, lard or butters) and a little castor is a common pattern.
What kind of oils can I use to make soap? Most natural plant oils and animal fats can be saponified, but each needs its own lye amount, which is why a lye calculator is essential. Ordinary cooking oils are a common starting point.
What do the Amish use to make soap? Traditional homestead soap was often made from rendered animal fat such as lard or tallow. Methods vary by household, so treat this as a general historical pattern.