Propylene glycol and ethylene glycol are different chemicals with different safety profiles. Propylene glycol (CAS 57-55-6) is FDA-approved as GRAS for food use under 21 CFR 184.1666. Ethylene glycol (CAS 107-21-1) is not food-approved and is classified as harmful if swallowed. Ethylene glycol transfers heat more efficiently; propylene glycol is used wherever incidental human or food contact is possible.
What is the difference between propylene glycol and ethylene glycol?
The two are chemically related but not interchangeable. Ethylene glycol is a two-carbon diol with the formula C2H6O2. Propylene glycol is a three-carbon diol with the formula C3H8O2, also called 1,2-propanediol.
The practical difference is toxicity. Ethylene glycol carries the GHS hazard statement H302, “Harmful if swallowed,” and NIOSH lists its target organs as the eyes, skin, respiratory system, and central nervous system. Propylene glycol is affirmed by the FDA as Generally Recognized As Safe (GRAS) as a direct food ingredient, and the majority of companies notifying the ECHA C&L Inventory report that it does not meet GHS hazard classification criteria.
The second practical difference is thermal performance. Ethylene glycol has lower viscosity and better heat-transfer efficiency than propylene glycol at the same concentration, which is why it dominates automotive and closed-loop industrial cooling. Propylene glycol trades some of that efficiency for a far more forgiving safety profile.
How do propylene glycol and ethylene glycol compare on physical properties?
All values below are the experimental constants published by PubChem and the NIOSH Pocket Guide to Chemical Hazards.
| Property | Propylene glycol | Ethylene glycol |
|---|---|---|
| CAS Number | 57-55-6 | 107-21-1 |
| Chemical formula | C3H8O2 | C2H6O2 |
| Other names | 1,2-Propanediol, MPG | 1,2-Ethanediol, MEG, monoethylene glycol |
| Molecular weight | 76.09 g/mol | 62.07 g/mol |
| Density at 20 °C | 1.0361 g/cm3 | 1.1135 g/cm3 |
| Weight per US gallon | 8.65 lb/gal | 9.29 lb/gal |
| Boiling point | 187.6 °C (370.8 °F) | 197.3 °C (387.7 °F) |
| Melting / freezing point | −59 °C (−76 °F) | −12.7 °C (9 °F) |
| Flash point (closed cup) | 99 °C (210 °F) | 111 °C (232 °F) |
| Vapor pressure at 20 °C | 0.08 mmHg | 0.06 mmHg |
| Water solubility | Miscible | Miscible |
| OSHA PEL | None established | None established |
| Food contact status | GRAS, 21 CFR 184.1666 | Not approved for food use |
Both glycols are combustible rather than flammable. Ethylene glycol is classed by NIOSH as a Class IIIB combustible liquid, with a lower explosive limit of 3.2% and an upper explosive limit of 15.3%. Propylene glycol’s 210 °F closed-cup flash point places it in the same Class IIIB range. Neither requires flammable-liquid storage cabinets, which is a meaningful difference from solvents like acetone or ethanol.
Need to convert between gallons, pounds, and drums for a specific fill? Use the RightPath chemical density and volume calculators.
Which glycol is toxic?
Ethylene glycol is the toxic one. It is sweet-tasting and readily ingested by animals and children, and the GHS classification assigned by the large majority of ECHA notifiers is H302, “Harmful if swallowed.” NIOSH lists symptoms of exposure as eye, skin, nose, and throat irritation; nausea, vomiting, and abdominal pain; weakness, dizziness, stupor, convulsions, and central nervous system depression; and skin sensitization. Ingestion requires immediate medical attention.
Propylene glycol is the low-toxicity alternative. The FDA permits it in food at levels not exceeding current good manufacturing practice, with maximum served levels of 5% in alcoholic beverages, 24% in confections and frostings, 2.5% in frozen dairy products, 97% in seasonings and flavorings, 5% in nuts and nut products, and 2.0% in all other food categories.
Neither chemical has an OSHA permissible exposure limit. That is not a statement that either is harmless — it means airborne exposure is not the governing hazard. Always work from the product-specific Safety Data Sheet, which you can pull from the RightPath SDS library.
Is propylene glycol food safe?
Yes, within the limits of 21 CFR 184.1666. The FDA lists propylene glycol as an anticaking agent, humectant, processing aid, solvent and vehicle, stabilizer and thickener, surface-active agent, and texturizer. USP and food-grade propylene glycol are the correct specifications for those uses; industrial-grade propylene glycol is not.
Ethylene glycol has no equivalent food clearance and must never be substituted into a food, beverage, pharmaceutical, or cosmetic process. If your application involves any credible path to human ingestion — brewery and winery chillers, food-plant refrigeration loops, ice rinks over food-service areas, HVAC coils in commercial kitchens — propylene glycol is the specification.
Which glycol should you use for your application?
| Application | Typical choice | Why |
|---|---|---|
| Automotive and engine antifreeze | Ethylene glycol | Best heat transfer, lowest cost per unit of freeze protection |
| Industrial chillers, data center cooling | Ethylene glycol | Closed loop, no food or human contact, efficiency matters |
| Brewery, winery, and food-plant glycol loops | Propylene glycol (USP/food grade) | Incidental food contact is possible |
| Food, flavor, and beverage formulation | Propylene glycol (USP/food grade) | GRAS under 21 CFR 184.1666 |
| Cosmetics and personal care | Propylene glycol (USP) | Humectant and solvent; skin contact expected |
| Pharmaceutical formulation | Propylene glycol (USP) | Compendial grade required |
| Aircraft and runway deicing | Propylene glycol | Lower aquatic and wildlife toxicity in runoff |
| Polyester resin and PET manufacturing | Ethylene glycol | Direct chemical feedstock |
| Solar thermal and geothermal loops | Propylene glycol (inhibited) | Potable-water proximity in many installs |
For deeper coverage of each product, see What Is Propylene Glycol Used For? and the Ethylene Glycol Safety and Properties buyer’s guide.
What grades and sizes does RightPath stock?
RightPath Industries is a Pittsburgh-headquartered bulk chemical distributor carrying over 8,000 chemicals, and stocks both glycols across industrial and compendial grades.
| Product | Grades stocked | Packaging |
|---|---|---|
| Propylene Glycol (1,2-Propanediol) | USP, food grade, industrial/technical, inhibited | 5-gal pails, 55-gal drums, 275/330-gal IBC totes, tank truck |
| Ethylene Glycol, Low Iron & Chloride | Industrial, low-iron/low-chloride, inhibited | 55-gal drums, 275/330-gal IBC totes, tank truck, railcar |
Related glycols including diethylene glycol, triethylene glycol, dipropylene glycol, hexylene glycol, and the full glycol ether range are listed on the bulk glycol supplier page. Not sure which container size fits your draw rate? See Drum vs IBC Tote vs Bulk.
How do you order propylene glycol or ethylene glycol from RightPath?
- Confirm the grade your process requires — USP or food grade for any ingestion pathway, industrial or inhibited for closed loops.
- Tell us the annual or monthly volume and the delivery point so freight is priced into the quote, not added after.
- Request bulk pricing and receive an all-in landed-cost quote, typically same day.
- Request the SDS and Certificate of Analysis before first shipment. See how to read a COA.
Frequently asked questions
Can propylene glycol replace ethylene glycol in an existing system?
Usually yes, but not at the same concentration. Propylene glycol is more viscous and transfers heat less efficiently, so a system converted from ethylene glycol typically needs a higher glycol percentage and may need pump or flow-rate adjustment to hold the same duty. Flush and verify inhibitor compatibility before switching.
Is propylene glycol the same as antifreeze?
Propylene glycol is one of the two glycols used to make antifreeze. Conventional automotive antifreeze is ethylene glycol based. “Pet-safe” or “food-grade” antifreeze is propylene glycol based. Both are sold as inhibited concentrates containing corrosion-inhibitor packages, not as pure glycol.
Which glycol has a lower freezing point?
Pure propylene glycol freezes at −59 °C (−76 °F) versus −12.7 °C (9 °F) for pure ethylene glycol. In practice both are used as water solutions, and freeze protection depends on the glycol concentration and the specific inhibited formulation, so use the manufacturer’s freeze-point curve for your product.
Does ethylene glycol require hazmat shipping?
Ethylene glycol is a Class IIIB combustible liquid with a 232 °F closed-cup flash point, well above flammable-liquid thresholds. Shipping classification depends on the specific formulation and inhibitor package, so confirm against the product SDS Section 14. For general background see DOT hazmat classes for solvents.
What is MEG?
MEG stands for monoethylene glycol, which is the same chemical as ethylene glycol (CAS 107-21-1). The “mono” distinguishes it from diethylene glycol (DEG) and triethylene glycol (TEG), which are heavier oligomers used in gas dehydration and plasticizers. MPG is the equivalent abbreviation for monopropylene glycol.
Authoritative sources
- PubChem CID 174 — Ethylene glycol
- PubChem CID 1030 — Propylene glycol
- NIOSH Pocket Guide to Chemical Hazards — Ethylene glycol
- 21 CFR 184.1666 — Propylene glycol (FDA GRAS)
Need a quote? Request bulk pricing from RightPath Industries for propylene glycol or ethylene glycol in drums, totes, tank truck, or railcar.