Every bar of soap is an argument between four properties that can’t all be maximised at once: hardness, lather, mildness, and how long it lasts. The oils you choose are how you settle that argument.
Here’s what each one actually contributes.
Olive
What it does: mild, conditioning, very low lather, soft bar.
Olive oil is mostly oleic acid, a long unsaturated fatty acid that makes a soap so gentle it’s traditionally used on babies. A 100% olive bar — Castile — is the mildest soap you can make.
It’s also close to useless on its own for the first year. Pure Castile takes six to twelve months to cure hard, and even then produces a low, slimy lather with almost no bubbles.
So olive is the base you build on. It’s 45–55% of most of our bars, and everything else in the recipe is there to fix what olive can’t do.
Coconut
What it does: hard bar, big lather, works in hard water, strips your skin.
Coconut is mostly lauric and myristic acid — short, saturated, and they produce the huge fluffy lather people associate with soap. It’s the only common oil that lathers properly in hard or salt water.
The catch is that the same short-chain structure that makes those bubbles also dissolves your skin’s own oils. A 100% coconut bar is a superb laundry and dish soap and unpleasant on a body.
The industry answer is superfatting — leaving unreacted oil in the bar. We keep coconut at 20–25% and superfat 5%, which is the standard compromise and a real one. Push coconut above 30% and you feel it.
Palm
What it does: hardness and stable lather without coconut’s harshness.
Palm is mostly palmitic acid, which makes a hard bar with a dense, long-lasting lather. It sits between olive and coconut and does the job neither can — hardness without stripping.
It’s also the ingredient with a genuine ethical problem attached. Palm oil expansion has driven deforestation across Southeast Asia at a scale nothing else in a soap recipe comes close to.
We use RSPO Mass Balance certified palm at 20–25%. That certification is imperfect — Mass Balance means certified and non-certified oil are mixed in the supply chain, so you’re funding certified production rather than receiving it. It’s the honest middle option between Segregated (better, considerably more expensive, hard to source in our volumes) and uncertified (no).
We’ve tried building the line palm-free. Twice. Both times the bars were either too soft or we had to push coconut high enough to be harsh. Some makers replace it with tallow, which we do in some products — but a palm-free vegan bar that’s still hard and mild is a harder problem than it looks.
Tallow
What it does: what palm does, from an animal.
Beef tallow is also palmitic-and-stearic-heavy, and it makes a hard, mild, creamy bar. Historically it was soap — before palm was cheap and global, western soap was tallow and lye, and it was good.
We use it in the Cedar & Tallow lotion bar and the Woodsman’s Hand Salve rather than in the soap. In a leave-on product tallow does something plant butters don’t quite match: its fatty acid profile is close enough to human sebum that it absorbs and seals unusually well. On knuckles that split every February, nothing we’ve tried works better.
Ours is grass-fed from a butcher two hours south, and it’s a by-product either way.
If that’s not for you, the Balsam & Shea Body Butter does a similar job entirely plant-based.
Shea and cocoa butter
What they do: superfat, mostly.
These go in at 5–8% and their job is to survive. Both are high in stearic acid and unsaponifiables — compounds that don’t react with lye at all and stay in the finished bar as free butter.
That unreacted fraction is most of why a handmade bar doesn’t leave your skin feeling tight. It’s also expensive, which is why commercial “shea butter soap” often contains under 1% of it.
Cocoa butter makes a harder bar; shea makes a more conditioning one. Cocoa carries a faint chocolate note that has to be worked around, which is why it’s in Tamarack & Amber and not in Wild Mint.
Castor
What it does: the thing that makes lather stick around.
Castor oil is 90% ricinoleic acid, which is unusual — it boosts and stabilises lather without contributing hardness or harshness. At 5% it turns thin bubbles into a dense persistent foam. At 15% it makes a sticky bar that never fully dries.
It’s the smallest ingredient with the most visible effect, and it’s in nearly everything we make.
A worked example
Balsam Fir & Birch Tar:
| Oil | % | Doing what |
|---|---|---|
| Olive | 48 | Mildness, the base |
| Coconut | 22 | Lather and hardness |
| Palm (RSPO) | 20 | Hardness without harshness |
| Shea butter | 5 | Superfat, conditioning |
| Castor | 5 | Lather stability |
Superfat 5%, water discount 10%. Six-week cure.
Nothing in that table is exotic. Move any number by five points and you get a noticeably different bar — more coconut and it strips, more olive and it’s soft, drop the castor and the lather collapses in the shower.
That’s the whole craft, really. Not secret ingredients. Just a table of percentages that somebody spent a long time getting wrong before they got it right.