Caustic Soda (Sodium Hydroxide): Grades, Concentrations, and Why Its Price Follows Chlorine

Market data current as of July 2026. Chemistry and grade guidance are evergreen.

Caustic soda is one of the few industrial chemicals whose price is set almost entirely by demand for something else. If you buy it, that single fact explains more about your invoice than any caustic soda forecast will.

What caustic soda actually is

Caustic soda and sodium hydroxide are the same compound: NaOH. "Caustic soda" is the industrial and commercial name and "sodium hydroxide" the chemical one. "Lye" commonly refers to NaOH too, but the word is not a unique chemical identity: it can also refer to potassium hydroxide (KOH), especially in soapmaking. Check the formula as well as the concentration and grade on any specification.

It is supplied two ways: as a solid (flakes, beads, or prills, typically 98–99% NaOH) or as an aqueous solution, most commonly at 50% or diluted to lower strengths. Solid is cheaper to ship per unit of NaOH because you are not paying freight on water; solution is easier to meter, dissolve, and handle without generating dust.

How it is made — and why that matters to your price

Caustic soda comes from the chlor-alkali process: electrolysis of brine (sodium chloride in water). Passing direct current through the cell splits the salt and water into three products at once.

Read that equation as a commercial constraint, not just a chemical one. Chlorine, hydrogen, and sodium hydroxide are produced in a ratio fixed by atomic mass. You cannot dial it. You cannot make caustic soda without simultaneously making chlorine.

The arithmetic is exact. One mole of Cl₂ weighs 70.90 g; the two moles of NaOH produced alongside it weigh 80.00 g. So:

This is the single most useful thing a caustic soda buyer can understand. A chlor-alkali plant does not decide how much caustic soda to make. It decides how hard to run its cells — and that decision is usually driven by chlorine, because chlorine is the harder product to place.

Why caustic soda pricing follows chlorine, not caustic soda

Chlorine is difficult and expensive to store at scale. Caustic soda solution can sit in a tank; chlorine largely has to be consumed as it is produced, and its dominant outlet is vinyls — ethylene dichloride (EDC) and then PVC. That makes ethylene availability the effective throttle on the entire chlor-alkali system.

When ethylene gets scarce, vinyls producers cut rates. Chlorine has nowhere to go. Chlor-alkali plants throttle back. And caustic soda — which nobody's demand changed — gets tight anyway.

That is precisely what played out across global markets in the first half of 2026. Disruption to Middle East supply reduced naphtha availability in Asia, and Asian cracker utilization fell from roughly 83% in February to 57% in May. Ethylene output dropped, vinyls producers curtailed, and an estimated 6–9% of global vinyls capacity was disrupted. Caustic soda tightened as a downstream consequence.

Note what is absent from that explanation: any change in how much caustic soda the world wanted. The tightness was transmitted entirely through the chlorine side of the equation.

The 2026 picture: tight globally, soft domestically

Here is where buyers most often misread the market. Global caustic soda tightness and US caustic soda pricing have been pointing in opposite directions through 2026, and headlines about one are routinely mistaken for signals about the other.

The practical takeaway for a US buyer: a headline about Asian force majeure is not automatically a reason to pre-buy domestically. Through mid-2026, US fundamentals were driven by soft consumption in pulp and paper, textiles, soaps, and water treatment, with availability improving into the third quarter as maintenance turnarounds completed. Those are different markets with different clocks.

Concentrations: choosing the right strength

Concentration is a handling and logistics decision at least as much as a chemical one. Buying 50% and diluting on site means paying freight on less water, but it requires dilution capability and a heated or trace-heated environment in cold weather — 50% NaOH solution begins to crystallize near 12 °C (about 54 °F). Buying pre-diluted removes that step entirely.

Grades: Technical, ACS, and Membrane

Grade describes purity and the documentation behind it. Paying for a tighter grade than your process needs is one of the most common avoidable costs in chemical procurement — and buying below what your process needs is one of the most expensive.

A practical rule: if your specification, SOP, or test method names a grade, match it exactly. If it does not, technical grade is usually correct and materially cheaper. If you are unsure which your process requires, ask us for the specification sheet and compare it against your method before ordering — that comparison takes minutes and routinely saves four figures on a drum-scale purchase.

Diluting 50% caustic soda: the arithmetic

Most buyers purchasing at volume buy 50% solution and dilute on site, because at 50% you are not paying freight on water you already have. The dilution math is a straight mass balance — no correction factors, no chemistry beyond bookkeeping.

To make a target concentration C from 50% stock, every 100 kg of finished solution needs:

Two things the table does not tell you. First, dilution is exothermic: adding 50% caustic to water releases heat, and doing it quickly in an unvented or undersized vessel can drive the temperature up fast. Add caustic to water, never the reverse, and control the rate. Second, these are mass ratios, not volume. Caustic solutions are considerably denser than water, so measuring by volume without correcting for density will give you the wrong strength.

Approximate densities at 20 °C

Treat these as planning figures for sizing tanks and estimating freight. For anything that has to hit a specification, work from the density stated on the lot Certificate of Analysis rather than a table — we include one with every order.

Cold weather: why 50% sets up in the tank

Caustic soda solutions crystallize at temperatures that depend sharply on concentration, and 50% is close to the worst case. Published crystallization points for 50% material vary between roughly 4 °C and 12 °C (about 40–54 °F) depending on the exact assay and the source consulted, which is precisely why unheated outdoor storage of 50% is a recurring winter problem: the material can begin dropping solids well before anything freezes in the ordinary sense.

You have two practical options. Trace-heat and insulate the tank and lines, or buy a lower concentration that stays liquid at your ambient temperature. A 25% or 30% solution is far more forgiving in an unheated space, and for many cleaning and pH-adjustment duties it is what the process wanted anyway. If you are in a cold climate and have been fighting crystallization in a 50% tank every January, the cheaper fix is usually the lower concentration, not the heat tracing.

Materials: what caustic soda attacks

The aluminium interaction is the one that causes real incidents. Caustic reacts with aluminium to liberate hydrogen, which is flammable and which accumulates in the headspace of a closed container. An aluminium tote, funnel, or scoop is not a minor material substitution here. Confirm compatibility against your Safety Data Sheet and your own engineering standards before selecting anything for storage or transfer.

What “lye” means on a chemical label

"Lye" is a common name, not a formula. It often means sodium hydroxide, including many products sold for soapmaking, food processing, and drain maintenance. But it may also mean potassium hydroxide in soapmaking. A product identified as NaOH is the same compound whether it is marketed as caustic soda or sodium-hydroxide lye; after confirming the formula, compare grade, concentration, assay, and documentation.

Two points regularly cause confusion:

• Sodium hydroxide makes bar soap; potassium hydroxide makes liquid soap. The saponification reaction is the same in kind, but NaOH yields hard sodium soaps and KOH yields softer potassium soaps. Substituting one for the other without recalculating will not produce the product you intended, because the two have different molar masses.
• Concentration and grade are separate questions from intended use. If your application has a documentation requirement, buy against that requirement and keep the paperwork. We supply a lot-specific Certificate of Analysis and a GHS-aligned Safety Data Sheet with every order, which is usually what the requirement actually is.

Sodium hydroxide vs potassium hydroxide

On a pure-material basis, KOH is heavier per mole, so equivalent alkalinity needs about 1.40 times the mass of KOH that it would of NaOH (56.11 ÷ 40.00). Real formulations must also account for the stated assay or purity of each product. That ratio, plus the price difference, is why NaOH is the default wherever the potassium ion is not specifically wanted. We stock potassium hydroxide flakes where it is.

Handling and storage

Sodium hydroxide is corrosive to skin, eyes, and many metals. A few properties drive most real-world handling decisions:

• Dissolution releases significant heat. Adding flakes to water is strongly exothermic and can raise solution temperature rapidly. Always add caustic to water, never water to caustic, and control the addition rate.
• It attacks aluminium, zinc, and tin, generating hydrogen gas. Use compatible materials — carbon steel, stainless, or appropriate plastics — for storage and transfer.
• 50% solution crystallizes near 12 °C. Unheated outdoor storage in cold climates will cause it to set up in tanks and lines.
• It absorbs carbon dioxide from air, gradually forming sodium carbonate. Keep containers closed to preserve titre in analytical applications.

For airborne exposure, OSHA's permissible exposure limit for sodium hydroxide is 2 mg/m³, and NIOSH sets the concentration immediately dangerous to life or health at 10 mg/m³. Those numbers matter most where dust is generated — handling flakes, charging a makeup tank — rather than where a solution sits closed in a drum.

Consult the Safety Data Sheet for the specific product and concentration before handling, and follow your site's engineering controls and PPE requirements. We provide a current SDS and a lot-specific Certificate of Analysis with every product.

Caustic soda from Alliance Chemical

We stock the full concentration and grade ladder from our Texas facility, from 5% dilutions through 50% solution and dry flakes, in container sizes from bottles to totes.

Technical and ACS grades are also stocked at 5%, 10%, 15%, 20%, and 30%. If you need a strength between these, tell us the target and we will quote the nearest stocked dilution or a custom blend.

Related guides

• Sodium Hydroxide for Precision Optical Cleaning — concentration and contact-time selection for high-purity cleaning.
• Neutralizing Spent Sodium Hydroxide Baths — what to do with caustic after the process is finished with it.