Every soaping oil carries a temperament. Long before modern fatty-acid charts, the old soapmakers knew their fats by feel: tallow for a firm, lasting bar; olive for a gentle one; coconut for a lather that leapt up in cold water. This cheat sheet gathers that working wisdom into one place, so you can read a recipe and sense the bar it will become.
How to read an oil
A finished bar is the sum of its fats. A few traits do most of the talking:
- Hardness — how firm and long-lasting the bar is.
- Cleansing — how briskly it strips oils; high numbers can feel drying.
- Lather — the fluffy bubbles versus the dense, creamy condition.
- Conditioning — the silky, skin-loving feel left behind.
No single oil excels at all of these, which is precisely why we blend.
The hard-bar and bubble oils
Coconut oil
The workhorse of bubbles. It hardens the bar and throws a big, airy lather even in hard water. Pushed too high it can feel stripping, so most makers keep it modest and lean on a generous superfat to soften its bite. See our note on superfat for the why.
Palm oil (and palm-free swaps)
Palm lends hardness and a stable, creamy lather, long prized as a tallow stand-in. If you would rather skip it, palm-free bars can still lather beautifully with the right blend of butters and harder oils.
Tallow and lard
The heritage fats. They build a hard, mild, low-cost bar with a dense, lotion-like lather — the backbone of cottage soap for centuries.
The gentle and conditioning oils
Olive oil
The soul of a Castile bar: exceptionally mild and conditioning, with a low, slippery lather. It traces slowly and the bar cures hard given patience.
Sweet almond, sunflower and other soft oils
These liquid oils add silkiness and conditioning. Used in excess they soften the bar and shorten its life, so treat them as the seasoning rather than the stew.
Shea and cocoa butter
Butters bring hardness and a luxurious, protective feel. Cocoa butter firms the bar noticeably; shea leans conditioning. A little carries a long way.
A word on the numbers, and on lye
Treat every SAP value and quality score as an estimate. Oils vary by harvest, region and freshness, so always run a recipe through a lye calculator and make a small test batch before committing a full pot.
Always add lye to water, never water to lye — the reverse can erupt. Wear goggles and gloves, and work in good ventilation.
Soapmaking lye (NaOH for bars, KOH for soft and liquid soaps) is caustic and deserves steady respect. If you are new to it, read our safety guide first, then return to the cupboard and start blending with confidence.