Inhibited and uninhibited glycol are different purchases

The base chemical is the smaller half of the product

Dow describes DOWFROST as 96.0 percent food grade propylene glycol plus food grade corrosion inhibitors, and DOWFROST HD as 94.0 percent propylene glycol with, in Dow’s words, “a specially designed package of industrial corrosion inhibitors.” Two products, one base chemical, two different inhibitor packages and two different glycol percentages. Nothing in the phrase “propylene glycol” distinguishes them, and nothing in it distinguishes either from a glycol supplied with no inhibitor at all.

That is the whole distinction. Uninhibited glycol is a chemical: it has a CAS number, an assay and a set of physical properties. An inhibited glycol is a formulation: a glycol, plus additives whose identity and concentration are usually the formulator’s, plus a claim about what that combination does in a metal system over time. The evidence you can obtain for the two is not the same kind of evidence, so the request you send a supplier should not be the same request.

What an inhibitor package is not

It is not a property of the glycol. Propylene glycol’s own records describe a stable material that, in the words of the Hazardous Substances Data Bank entry aggregated by PubChem, “at high temperatures, in the open, tends to oxidize, giving rise to products such as propionaldehyde, lactic acid, pyruvic acid, and acetic acid.” Those acids are part of what an inhibitor package is buffering against. A fluid that has consumed that buffer still contains glycol; it is no longer the product that was purchased.

It is not permanent either, and a federal design criterion says so plainly. UFC 3-410-01 §2-13.7 instructs designers to minimise the use of antifreeze in ground loops, to use propylene glycol where antifreeze is necessary, to keep concentrations to a minimum, and to “Coordinate glycol concentration with manufacturer to mitigate corrosion inhibitor degradation.” The criterion treats the inhibitor as something that degrades and as something coupled to concentration — which is why a purchase request that states only a freeze point has not stated the requirement.

And it is not transferable. A protection table, an inhibitor description or a service-life statement published for one named formulation is evidence about that formulation. A nominal grade or concentration does not establish interchangeability between products or between suppliers.

• Is the material being quoted a glycol, or a formulated inhibited fluid?
• If it is inhibited, which named formulation, and at what glycol percentage on which basis?
• Is it supplied ready to use or as a concentrate, and what dilution water does the manufacturer require?
• Who approves the choice, and does an existing fill constrain it?

Write the request so a quote can answer it

Our suggested request names four things together: the exact product or specification, the concentration with its basis and reference temperature, whether the material is a concentrate or ready to use, and the protection objective the equipment owner actually requires. Ask separately for the current technical data revision rather than accepting a figure quoted from memory or from a distributor page.

Where the answer is “uninhibited glycol,” record that as the answer rather than as a gap. There are systems and processes for which an uninhibited glycol is exactly what the specification calls for. What must not happen is a request written as though the two were the same line item, priced against each other, and then filled with whichever was cheaper. Alliance does not tell you which your system needs; the equipment owner and the responsible engineer do.

Requirement → evidence → decision boundary

An editorial checklist for your review—not a table of product specifications.

Revision record

1.0 · September 12, 2026 — Source-based editorial edition. No original testing or product qualification is claimed.

For engineering and purchasing teams defining closed-loop fluid requirements. This collection does not size a ground loop, prescribe a concentration, or approve a substitution.