Propylene Glycol vs Ethylene Glycol: The Complete Buyer's Guide
Table of Contents
What you will learn
📋 What You'll Learn
This guide walks you through propylene glycol vs ethylene glycol: the complete buyer's guide with detailed instructions.
The only glycol guide you need
PG vs EG. Inhibited vs technical vs USP. Every concentration, every grade, every application — decoded for chemical buyers and facility engineers.
Glycols are the workhorses of heat transfer, freeze protection, and process cooling. But choosing the wrong type, grade, or concentration can mean equipment corrosion, regulatory violations, or thousands of dollars in wasted product. This guide breaks down everything a chemical buyer needs to know.
Propylene Glycol vs Ethylene Glycol: The Core Decision
Every glycol selection starts here. Both transfer heat. Both protect against freezing. But they serve fundamentally different markets.
Propylene Glycol (PG)
- Low toxicity — GRAS-listed (Generally Recognized as Safe) by the FDA
- Food/beverage safe — Used in food processing lines, breweries, wineries
- Required by code in HVAC systems serving occupied buildings
- Slightly lower heat transfer efficiency than EG
- Higher viscosity — needs slightly more pump energy
Ethylene Glycol (EG)
- Superior heat transfer — more efficient at every concentration
- Lower viscosity — less pumping energy required
- Better freeze protection per volume of glycol
- Toxic if ingested — not suitable for food contact systems
- Automotive/industrial standard for closed-loop systems
Use PG when the system is in a food facility, an occupied building, or anywhere a leak could contact people or products. Use EG for automotive, industrial chillers, ground-source heat pumps, and closed systems where human contact is not a concern.
Freeze Point by Concentration
The concentration you need depends entirely on the minimum ambient temperature your system will face. Under-dosing means frozen pipes. Over-dosing wastes money and reduces heat transfer efficiency.
| Concentration | PG Freeze Point | EG Freeze Point | Best For |
|---|---|---|---|
| 30% | +5 °F (-15 °C) | -5 °F (-20 °C) | Mild climates, seasonal protection |
| 40% | -13 °F (-25 °C) | -17 °F (-27 °C) | Most HVAC/chiller systems |
| 50% | -28 °F (-33 °C) | -34 °F (-37 °C) | Cold climates, outdoor equipment |
| 60% | -48 °F (-44 °C) | -52 °F (-47 °C) | Extreme cold, Arctic conditions |
| 100% (neat) | Gel at +21 °F | Gel at +9 °F | Dilute on-site for custom concentration |
100% (neat) glycol actually has a higher freeze point than diluted solutions. A 60/40 glycol-to-water ratio gives maximum freeze protection. Going above 60% glycol provides diminishing returns and reduces heat transfer.
Understanding Glycol Grades
Not all glycol is the same purity, and the grade you need depends on your application and regulatory requirements.
| Grade | Purity | What It Means | Use Cases |
|---|---|---|---|
| Inhibited | 99%+ | Contains corrosion inhibitors to protect metals in closed-loop systems | HVAC, chillers, boilers, automotive |
| Technical | 99%+ | Industrial purity, no inhibitor package — pure glycol | Manufacturing, deicing, non-metal systems |
| USP | 99.5%+ | Meets United States Pharmacopeia standards for pharmaceutical/food use | Food processing, cosmetics, pharma |
| ACS | 99.5%+ | Meets American Chemical Society reagent grade specifications | Laboratory, analytical, research |
| Semiconductor | 99.99%+ | Ultra-pure for electronic-grade applications | Semiconductor fabrication, cleanrooms |
If your glycol runs through any metal piping, heat exchangers, or pumps, you almost certainly want inhibited glycol. Uninhibited (technical grade) glycol becomes acidic over time and will corrode copper, steel, and aluminum. Corrosion inhibitors extend fluid life from 2-3 years to 5-10+ years.
Application Guide: Which Glycol for What
HVAC and Chillers
Photo by noe fornells on Unsplash
Most commercial HVAC systems in occupied buildings are required to use propylene glycol (inhibited) at 30-50% concentration. The inhibitor package protects the copper and steel components in the loop. For systems that never contact people or food — like ground-source heat pump loops — ethylene glycol 50/50 offers better thermal performance.
Automotive and Fleet
Photo by Mathias Reding on Unsplash
Automotive coolant is almost always ethylene glycol-based. 100% ethylene glycol inhibited can be diluted to the concentration your climate requires. For pre-mixed convenience, Arctic Assist 50/50 is ready to pour.
Food and Beverage Processing
Photo by Luo Jin Hong on Unsplash
Any glycol in a system that could contact food must be propylene glycol USP grade. This is non-negotiable per FDA 21 CFR. Breweries, wineries, dairy plants, and food manufacturers use PG in jacketed tanks, glycol chillers, and process cooling lines. Available in 30%, 40%, and 50% USP pre-mixed concentrations.
Laboratory and Research
Lab applications demand traceable purity. Ethylene glycol ACS grade and propylene glycol inhibited ACS grade meet American Chemical Society reagent specifications for analytical work, calibration baths, and reaction media.
Semiconductor and Cleanroom
Ethylene glycol semiconductor grade is ultra-purified for applications where trace metals and particulates must be at parts-per-billion levels. Used in wafer fabrication cooling loops and cleanroom environmental controls.
Deicing and Winterization
For winterizing pipes, RVs, sprinkler systems, and outdoor equipment, 50% PG technical grade provides freeze protection to -28 °F without the cost of inhibitors or USP certification. Arctic Assist is formulated specifically for freeze protection applications.
Specialty Solvents (Glycol Ethers)
Glycol Ether EE and Glycol Ether EE ACS are not heat-transfer fluids — they are solvents derived from glycols. Used in coatings, inks, cleaning formulations, and as coupling agents in water-based systems. PEG 200 serves as a lubricant, humectant, and carrier in pharmaceutical and personal care formulations.
How to Choose the Right Concentration
Selecting the right glycol concentration involves balancing three factors:
- Freeze protection — What is the lowest temperature your system will experience?
- Heat transfer efficiency — Higher glycol concentrations reduce thermal conductivity
- Viscosity and pump load — More glycol means thicker fluid and more pump energy
The sweet spot for most systems is 30-50%. Beyond 60%, you get minimal additional freeze protection but significantly worse heat transfer and higher viscosity.
Do not use 100% glycol undiluted as antifreeze. Pure glycol actually freezes at a higher temperature than a 50/50 or 60/40 mix. Water is essential to the freeze-depression mechanism. Buy 100% concentrate only if you plan to dilute it on-site to your target ratio.
Shop All Alliance Chemical Glycols
Propylene Glycol (13 Products)
Low toxicity. Food-safe grades available. HVAC, food processing, pharma.
Ethylene Glycol (7 Products)
Superior heat transfer. Automotive, industrial, semiconductor.
Glycol Ethers & Specialty (5 Products)
Solvents, freeze protection blends, and PEG for formulation.
Need help choosing?
Our team can recommend the right glycol type, grade, and concentration for your system. Every order includes full SDS documentation and Certificate of Analysis.
Contact SalesFrequently Asked Questions
What is the difference between propylene glycol and ethylene glycol?
Propylene glycol (PG) is low-toxicity and FDA GRAS-listed, making it safe for food contact systems. Ethylene glycol (EG) is toxic but offers superior heat transfer efficiency and lower viscosity. Use PG where safety matters; use EG where performance is priority in closed industrial systems.
What concentration of glycol should I use for freeze protection?
It depends on your minimum temperature. 30% glycol protects to about +5 degrees F (PG) or -5 degrees F (EG). 50% protects to -28 degrees F (PG) or -34 degrees F (EG). Do not use 100% glycol undiluted—a 50-60% mix provides better freeze protection than pure glycol.
What does inhibited glycol mean?
Inhibited glycol contains a corrosion inhibitor package that protects metals (copper, steel, aluminum) in closed-loop systems. Uninhibited glycol becomes acidic over time and corrodes metal components. Use inhibited glycol in any system with metal piping or heat exchangers.
What is USP grade propylene glycol?
USP (United States Pharmacopeia) grade means the propylene glycol meets pharmaceutical purity standards. It is required for any glycol in food processing, beverage production, cosmetics, or pharmaceutical applications. USP grade is certified to 99.5% or higher purity.
Can I use ethylene glycol in a food processing facility?
No. Ethylene glycol is toxic and must never be used in systems that could contact food or beverages. Food facilities must use propylene glycol USP grade per FDA regulations. This applies to jacketed tanks, glycol chillers, and any cooling loop in a food plant.
