Best oils for soap making: what olive, coconut, shea and others do
TUREFF• •0
The oils you choose decide almost everything about a bar of soap: how hard it is, how long it lasts, whether the lather is big and bubbly or small and creamy, and how it feels on skin. Most soap recipes blend several oils, because no single one does everything well. This guide explains what the common ones contribute so you can read recipes with understanding and adapt them sensibly.
The three things to balance
Soap makers usually think about a bar in terms of:
- Hardness: whether the bar stays firm and lasts, or turns soft and mushy.
- Cleansing and lather: how strongly it cleans and how much bubbly lather it makes.
- Conditioning: how mild and gentle it feels on skin.
These pull against each other. Oils that give strong cleansing and big bubbles can feel drying in large amounts; very conditioning oils make gentle but softer bars. A good recipe finds a balance.
Common oils and what they bring
- Olive oil: the classic soap oil. Gentle and conditioning, with a low, creamy lather. A bar made entirely or mostly of olive oil (often called Castile soap) is very mild but starts soft and is usually given a long cure to harden.
- Coconut oil: makes a hard bar with lots of fluffy, bubbly lather and strong cleansing power, even in cold or hard water. In high proportions it can feel drying, so it is usually one part of a blend rather than the whole thing.
- Palm kernel oil: behaves much like coconut oil, adding hardness and bubbles.
- Palm oil: adds hardness and a stable lather. Many makers avoid it or choose certified sustainable sources because of concerns about deforestation; plenty of recipes are palm-free.
- Shea butter: adds hardness and a creamy, conditioning feel. Usually used as a smaller part of the recipe.
- Cocoa butter: makes a hard, long-lasting bar. Unrefined cocoa butter carries a chocolate scent.
- Castor oil: used in small amounts to boost and stabilise lather. Too much makes a sticky, soft bar.
- Sweet almond, sunflower and rice bran oils: liquid oils that add conditioning. Oils high in certain unsaturated fats can go rancid sooner, which can show up as orange spots on the bar later on, so fresh oil and sensible proportions matter.
- Animal fats (lard and tallow): traditional choices that make hard, mild, long-lasting bars. Not suitable if you want a vegan soap.
Why the fatty acids matter
Each oil is a mix of fatty acids, and those fatty acids are what really decide the soap's properties. Lauric and myristic acids (plentiful in coconut and palm kernel) give big lather and cleansing. Palmitic and stearic acids (in palm, butters and animal fats) give hardness. Oleic and linoleic acids (in olive and many liquid oils) give conditioning. Ricinoleic acid, found mostly in castor oil, helps lather. Most lye calculators show estimated hardness, cleansing and conditioning numbers for your blend, built from these profiles.
Superfat in plain terms
Superfat means deliberately leaving a small proportion of the oils unreacted, by using a little less lye than would turn every last bit of oil into soap. It does two useful things:
- It leaves some free oil in the bar, which makes it feel milder.
- It gives a safety margin, so small errors in weighing or variation in oils are much less likely to leave excess lye in the soap.
A lye calculator lets you set the superfat, and it is built into the lye amount it gives you. Do not try to get the same effect by simply cutting the lye by eye; set it in the calculator so the numbers stay right. Very high superfats can make a bar soft, greasy or prone to going rancid.
Changing a recipe safely
If you swap one oil for another, the amount of lye needed changes. Always run any changed recipe through a lye calculator before you make it, and weigh everything on scales.
Which oils do you like in your bars, and what surprised you? Share your favourite combinations in the comments.