Executive Summary
Propylene glycol and ethylene glycol are the two most commonly used coolant base fluids in thermal management systems. Although similar in thermal performance, they differ in viscosity, material compatibility, safety, and handling considerations. This blog provides a clear comparison of their key physical properties—including freezing point, boiling point, viscosity, thermal conductivity, specific heat, material compatibility, and safety hazards—to help engineers make informed decisions when choosing between the two fluids for electronics cooling, battery systems, HVAC, or industrial applications.
1. Introduction
Propylene glycol–water and ethylene glycol–water mixtures are widely used in cold plates, liquid cooling loops, and industrial cooling applications. While both offer freeze protection and stable thermal performance, selecting the right fluid depends on the required temperature range, system pressure drop, materials used in the cooling loop, cost targets, and safety regulations.
The following sections summarize the key differences using data from a 50% glycol–water blend.
2. Key Property Comparison Table
| Property | Ethylene Glycol (50% by volume) | Propylene Glycol (50% by volume) |
| Freezing Point (°C) | -37 | -34 |
| Boiling Point (°C) | 107 | 106 |
| Viscosity (cP) | 22 (@ -18°C) 6.5 (@ 4°C) 2.8 (@ 27°C) 1.5 (@ 49°C) | 74 (@ -20°C) 19 (@ 0°C) 6.3 (@ 20°C) 2.3 (@ 50°C) |
| Specific Gravity | 1.1 (@ -18°C) 1.09 (@ 4°C) 1.08 (@ 27°C) 1.06 (@ 49°C) | 1.04 (@ 15°C) |
| Thermal Conductivity (W/m·K) | 0.4 (–30 to 100°C) | 0.4 (–30 to 100°C) |
| Specific Heat (kJ/kg·K) | 3.2 | 3.6 |
| Cost ($/gallon) | 25.8 | 29.3 |
| Safety Hazard | Highly toxic | Low toxicity |
3. Material Compatibility
Compatibility is rated as:
A = Recommended (little or no reaction)
B = Good option (minor reaction potential)
F = Not recommended (corrosion or strong reaction)
Ethylene Glycol Compatibility
• Commodity plastics — A
• Engineered thermoplastics — A
• Elastomers — A
• Aluminum — A
• Brass — A
• Copper — B
• Stainless steel — B
Propylene Glycol Compatibility
• Commodity plastics — B
• Engineered thermoplastics — B
• Elastomers — A
• Aluminum — B
• Brass — B
• Copper — A
• Stainless steel — B
4. Which Coolant Should You Use?
Ethylene Glycol (EG): Best for applications where cost, low viscosity, and strong thermal performance are priorities.
Propylene Glycol (PG): Preferred for systems requiring low toxicity, easier disposal, and safer handling—especially in consumer, medical, or regulated environments.
5. Conclusion
Both ethylene glycol and propylene glycol provide effective freeze protection and thermal performance. Ethylene glycol offers lower viscosity and lower cost, while propylene glycol provides superior safety and easier handling. Understanding the system’s material compatibility, operating temperature range, and regulatory requirements enables engineers to select the most appropriate coolant for reliable long-term operation.
About HeatSync
HeatSync is a Silicon Valley–based thermal engineering firm specializing in advanced air and liquid cooling solutions for electronics and battery systems. With nearly 150 years of combined experience, our team delivers end-to-end thermal design—architecture, simulation, digital twins, virtual sensors, and prototyping—for applications ranging from consumer electronics and EV batteries to AI servers and data-center infrastructure. Equipped with a full prototyping and reliability lab, HeatSync provides high-fidelity CFD modeling, multiphysics analysis, immersion and two-phase cooling development, thermal-mechanical validation, and performance optimization. We help companies accelerate innovation and build reliable, manufacturable, and energy-efficient thermal management systems.
Tags
propylene glycol, ethylene glycol, coolant comparison, liquid cooling systems, thermal management fluids, glycol-water mixtures, electronics cooling, battery cooling solutions, material compatibility, HeatSync insights