Best lye for soap making
Lye is a commodity chemical, so the brand matters far less than the grade, the packaging and how you store it. Here is what to actually look for.
For bar soap you want sodium hydroxide at 99% or higher purity, sold as beads in a sealed, resealable container — 143 g for a one-kilogram batch. Liquid soap needs potassium hydroxide instead, at 223 g for the same oils because it is heavier and only sold at about 90% pure. Beyond purity and packaging, one tub of lye is much like another.
Lye is one of the few soap ingredients where brand loyalty makes almost no sense. Sodium hydroxide is sodium hydroxide — a commodity chemical made to a spec, and a reputable supplier selling 99% beads is selling the same thing as the next one. What separates a good purchase from a bad one is the grade, the packaging and how quickly you can get more.
The first decision is which lye. Sodium hydroxide (NaOH) makes solid bars; Potassium hydroxide (KOH) makes liquid and soft soap. They are not interchangeable and the weights are not close: the same one-kilogram blend takes 143 g of sodium hydroxide or 223 g of potassium, because potassium is a heavier atom and flake KOH is only about 90% pure.
The second decision — and the one people get wrong — is the container. Lye pulls water out of the air, and a tub that does not reseal properly will quietly gain weight over a few months. That means every batch you weigh from it after that point is short of lye without you knowing. Run your own numbers through the lye calculator, then buy accordingly.
The two lyes
Worked on a one-kilogram beginner blend at the standard superfat. The last column is what almost nobody tells you — how many batches a tub actually gets you.
How much to buy
The sensible first purchase. Enough to learn on, small enough that it will be used up before it degrades.
Where the price per pound starts to matter. Only worth it if you are soaping often enough to get through it in a year.
At 5% superfat. Your own blend will differ — coconut-heavy recipes need noticeably more.
What to judge a lye on
Look for 99% or higher for sodium hydroxide, and treat a product that does not state a purity as unknown. A calculator assumes pure lye; if yours is 96% you are under-dosing by four per cent and will not know why the bars are soft.
Beads pour cleanly, dissolve predictably and do not throw dust the way flakes do. Flake lye is not worse chemically — it is just less pleasant to weigh out next to your face.
The single most important physical feature. A screw-top HDPE tub with a gasket keeps moisture out; a bag with a fold-over top does not. Lye that has absorbed water weighs more than the lye in it, so every batch after that point is short.
"Food grade" on lye usually indicates it is sold for pretzels and olives, and it is fine for soap. But it is a marketing distinction rather than a purity one: a 99% technical grade from a soap supplier is the same chemical.
Lye is restricted or awkward to ship in some places, and running out mid-project is worse than paying slightly more. A supplier that reliably has stock beats one that is cheaper twice a year.
Buying and storing it
A scale reading to 0.1 g matters more than which lye you bought. Lye measured by volume is how people get hurt, and a scale reading whole grams cannot hit a superfat target reliably.
Keep it in the container it came in, sealed, somewhere cool and dry — not the garage, not under the sink. Every transfer is a chance to spill it and an hour of exposure to humidity.
Sealed lye keeps for years. Opened lye starts absorbing moisture. Knowing a tub has been open eighteen months tells you to be suspicious of a batch that came out soft.
Goggles that seal, chemical-resistant gloves, and a dedicated stainless or HDPE jug. Not optional, and not something to improvise on the day the lye arrives.
Work out what your recipe needs
Enter your oils and superfat to see the lye weight, so you know what a tub actually buys you.
Open the lye calculator →Print the safety checklist
Lye handling, kit and the order of operations, on one page you can pin up where you work. Free.
Estimates, not advice. Every figure on this page is computed from published reference values and standard measures, so your own inputs, equipment and conditions will move it. Nothing here is professional advice — talk to a qualified professional before acting on it.