What Is Ethylene Glycol?

Ethylene glycol (EG), also known as monoethylene glycol (MEG) or ethane-1,2-diol (C₂H₆O₂), is a synthetic, water-soluble organic compound produced industrially by the hydration of ethylene oxide. It is a colorless, nearly odorless, viscous liquid with a faintly sweet taste. Ethylene glycol is acutely toxic if ingested and is not approved for use in food, pharmaceutical, or personal care products. It is primarily an industrial chemical used in antifreeze, heat-transfer fluid, and polymer manufacturing applications, where its high boiling point, low freezing point of aqueous mixtures, and good thermal stability are more important than food-safety requirements.

Industrial and Commercial Uses

Ethylene glycol is one of the most widely produced industrial chemicals in the world. Its high boiling point, good thermal stability, and complete miscibility with water make it well-suited for demanding heat-transfer and chemical manufacturing applications.

  • Automotive Antifreeze and Engine Coolant: The largest single use of EG worldwide. EG/water mixtures provide freeze protection, boiling-point elevation, and corrosion inhibition in internal combustion engine cooling systems. Most commercial antifreeze products are based on EG with an inhibitor package.
  • Aircraft De-Icing and Anti-Icing: Type I aircraft de-icing fluids are primarily heated EG/water solutions. Type II and IV fluids use thickened EG or propylene glycol formulations for longer holdover times. Ground equipment and runway de-icing also use EG-based products.
  • Industrial Heat Transfer: EG is used as the heat-transfer fluid in closed-loop industrial cooling systems, HVAC chillers, data center cooling, and solar thermal collectors in applications where food safety is not required. It provides freeze protection and boiling-point elevation under pressure.
  • Polyester Fiber and PET Resin Manufacturing: A major chemical feedstock. EG reacts with terephthalic acid to produce polyethylene terephthalate (PET), the polymer used in plastic bottles, food packaging, polyester textile fibers (Dacron, Terylene), and magnetic recording film.
  • Natural Gas Processing: EG is injected into natural gas pipelines and wellheads to prevent hydrate (ice-like solid) formation that can block flow. It is also used as a desiccant to dehydrate natural gas in glycol dehydration units.
  • Hydraulic Brake Fluids: Some DOT brake fluid formulations use EG as a base fluid component, valued for its high boiling point and hygroscopic behavior that keeps moisture distributed rather than pooled.
  • Electrolytic Capacitors: EG is used as a high-boiling-point solvent in the electrolyte of aluminum electrolytic capacitors, providing stable conductivity over a wide operating temperature range.
  • Chemical Intermediate: EG is a precursor to polyester resins, polyurethanes, di- and triethylene glycols, and ethylene glycol ethers used in paints, coatings, and cleaning products.
Typical Values — 99.5% Ethylene Glycol
Property Value Test Method
AppearanceClear, colorless viscous liquidVisual
Boiling Point197.3 °C (387 °F)ASTM D 1120
Freezing Point−13.0 °C (8.6 °F)ASTM D 1177
Flash Point (open cup)116 °C (241 °F)ASTM D 92
Density (20 °C)1.113 g/mLASTM D 1122
Viscosity (20 °C)18–20 cStASTM D 445
pH (50% v/v in distilled water)6.5 – 8.5ASTM D 1287
Water content (max)0.05%ASTM D 1123
Cubic Expansion Coefficient0.00057 1/K—
Alkaline Reserve0 ml HCl 0.1NASTM D 1121

Data from Dow Chemical "Ethylene Glycol Product Guide" and ASTM specification values for industrial-grade monoethylene glycol.

Non-Metal Compatibility with Ethylene Glycol

Chemical compatibility ratings for plastics, fluoropolymers, and elastomers in contact with ethylene glycol. Conditions of exposure and the presence of other chemicals or trace impurities should always be considered when selecting a construction material. Glycols are likely to leak past improperly assembled or defective fittings and seals.

Material Rating
ABSA — Excellent
CPVCA — Excellent
EPDMA — Excellent
Kel-F (PCTFE)A — Excellent
Neoprene (CR)A — Excellent
Nitrile (NBR)A — Excellent
Polypropylene (PP)A — Excellent
PTFE (Teflon)A — Excellent
PVDF (Kynar)A — Excellent
SiliconeA — Excellent
CeramicA — Excellent
Acetal (POM / Delrin)B — Good
TygonB — Good
FEPR — Resistant
HDPER — Resistant
Nylon 6 / 66R — Resistant
PolyurethaneR — Resistant
PVC Type IR — Resistant
PVC Type IIR — Resistant
Viton A (FKM)R — Resistant
Silica— — No Data
Rating Code (Non-Metals)
AExcellent — No effect
BGood — Minor effect
RResistant
CFair — Moderate effect
UUnsatisfactory
XConflicting data

Source: Geotech Environmental Equipment, Chemical Compatibility Reference Chart.

Corrosion Resistance — Metals (Pure Ethylene Glycol)

General guidance on metal corrosion rates in contact with pure ethylene glycol. Note that zinc is not compatible with ethylene glycol or its water mixtures — avoid zinc-coated or galvanized components. Corrosion inhibitor packages should always be used in EG/water systems to protect metals, particularly steel and aluminum.

Material Penetration Rate
AluminumE — <2 mils/year
Hastelloy CE — <2 mils/year
304 Stainless SteelG — <20 mils/year
316 Stainless SteelG — <20 mils/year
Carbon SteelG — <20 mils/year
BrassG — <20 mils/year
CopperG — <20 mils/year
Rating Code (Metals)
E<2 mils penetration/year — Excellent
G<20 mils penetration/year — Good
S<50 mils penetration/year — Marginal
U>50 mils penetration/year — Unsatisfactory

Source: Geotech Environmental Equipment, Chemical Compatibility Reference Chart.

Corrosion Table — Ethylene Glycol – Water Mixtures

Mixtures of Ethylene glycol and water are generally more corrosive than pure water, so corrosion inhibitor packages should be used to ensure circuit integrity over the service life of the system. The following table shows corrosion values for a 50% v/v Ethylene glycol – water mixture versus plain water, measured according to ASTM D 1384. Results for plain water are shown for comparison.

Values represent the average change in coupon weight in g/m². A positive number indicates a weight gain due to the formation of a stable, protective oxide layer on the metal's surface.

Material EG 50% v/v (g/m²) Water (g/m²)
Steel−225−76
Aluminium−68−32
Copper−1.2−1.0
Cast Iron−92−192
Brass−2.5−1.0
Solder−136−11

Negative values indicate mass loss (corrosion). Per ASTM D 1384 glassware corrosion test. Inhibited EG formulations will produce significantly better results than uninhibited pure glycol.

Elastomer Compatibility — EG–Water Mixtures

Elastomer compatibility ratings for Water/Ethylene Glycol (Hydrolube N0674-70) per Parker O-Ring Handbook ORD-5700. Ratings apply to the fluid mixture, not pure EG.

Elastomer Abbreviation Parker Rating
NitrileNBR1 — Excellent
Hydrogenated NitrileHNBR1 — Excellent
Ethylene PropyleneEPDM1 — Excellent
Fluorocarbon (Viton)FKM1 — Excellent
HifluorFKM1 — Excellent
PerfluoroelastomerFFKM1 — Excellent
Styrene-ButadieneSBR1 — Excellent
Neoprene / ChloropreneCR2 — Good
ButylIIR2 — Good
FluorosiliconeFVMQ2 — Good
SiliconeMQ, VMQ, PVMQ2 — Good
PolyacrylateACM4 — Not Recommended
PolyurethaneAU, EU4 — Not Recommended
Aflas (TFE/Propylene)FEPMX — Insufficient Data
ButadieneBRX — Insufficient Data
IsopreneIRX — Insufficient Data
Natural RubberNRX — Insufficient Data
HypalonCSMX — Insufficient Data
Parker Rating Code (ORD-5700)
1Excellent — Recommended for static and dynamic service
2Good — Satisfactory for static service
4Not Recommended — Severe effect
XInsufficient data available

Source: Parker Hannifin, O-Ring Handbook ORD-5700, fluid reference "Hydrolube-Water/Ethylene Glycol N0674-70".

Ethylene Glycol Property Calculators

Explore the full set of Ethylene glycol property calculators on KasperCalc:

Frost Protection Density Specific Heat Capacity Thermal Conductivity Viscosity Prandtl Number Thermal Expansion Coefficient Boiling Point

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