Substitutes for soap

Castor oil substitutes in soap

Castor oil is almost all ricinoleic acid, which no other common oil carries in quantity, so nothing replaces it: at 5 % it adds lather rather than hardness. Leave it out of the bar below and bubbly lather falls from 25 to 20 and creamy from 19 to 15, while the lye barely moves. More coconut oil in its place brings the bubbles back but not the creamy lather, and needs more lye.

The bar they are tried in

Castor oil5 %
Olive oil65 %
Coconut oil30 %

NaOH · 1000 g · Superfat 5 % 141.8 g

The bar: 5 % castor oil, at a 5 % superfat, for 1,000 g of oils. The rest: 65 % olive oil and 30 % coconut oil. As it is, it needs 141.8 g of sodium hydroxide.

Open the bar in the lye calculator

The substitutes, closest first

Substitute	Sodium hydroxide, g	With the lye left as it was
1Avocado oil	142.1	5.2 %barely moves
2Nothing in its place: olive oil takes its share	142.2	5.2 %barely moves
3Shea butter	141.9	5.1 %barely moves
4Coconut oil	144.4	6.7 %recalculate

With the lye left as it was: the superfat when the sodium hydroxide weighed for the bar as it is goes in with the substitute, planned at 5 %. Each lye figure opens that bar in the lye calculator, which works out the lye for it.

What each does to the bar

	Hardness	Cleansing	Conditioning	Bubbly lather	Creamy lather	Iodine value	INS	Linoleic and linolenic acid, %
As it is, with castor oil	35	20	61	25	19	62	148	9.2
Avocado oil	36	20	60	20	15	62	148	9.7
Nothing in its place: olive oil takes its share	36	20	60	20	15	62	148	9.5
Shea butter	37	20	59	20	17	60	150	9.2
Coconut oil	39	24	56	24	15	58	155	9.0
Usual range	29–54	12–22	44–69	14–46	16–48	41–70	136–165

Closest means the smallest total change across these figures, each counted against the width of its usual range, as the lye calculator’s swap suggestions count it. It is a convention, not a verdict on the bar: a butter that matches on paper can still melt lower, crack or smell, which the note above and the guides cover.

Guides

Substitutes for other oils

Where these numbers come from

Every figure here is worked out from the oil records, each with its sources on its own page: