03/04/2026 by Thomas Clark
Polyalkylene glycol (PAG) and polyol ester (POE) refrigeration oils are both types of synthetic lubricant employed to maintain compressors.
They are designed to lubricate moving components within the compressor, prevent against corrosion and wear, preserve seals and valves and be miscible with refrigerant used in cooling systems.
While they share commonalities, these two types of refrigeration compressor oil have key differences concerning their stability, electrical conductivity and moisture handling, and the application in which they are most often used.
In the following guide, we’ll explore each refrigeration oil in turn and explore what makes them different from each other.
What is PAG refrigeration oil?
PAG refrigeration oil is a lab-made lubricant employed in refrigeration systems using hydrofluorocarbon (HFC) refrigerant R134a and hydrofluoroolefin (HFO) refrigerant R1234yf.
Fully synthetic solutions, they are composed primarily of polymerised ethylene oxide and propylene oxide chains.
There are multiple types of PAG oil available based on oil viscosity like PAG150 PAG100 and PAG46 and the refrigerant type they mix effectively with.
Key characteristics of PAG oils
PAG refrigeration oils are characterised by outstanding thermal stability, exceptional anti-wear properties and a high viscosity index (180 to 250). They resist varnish and sludge formation, have low volatility and are highly hygroscopic.
What is POE refrigeration oil?
POE oil is a wax-free synthetic oil employed in refrigeration compressors using refrigerants R-134a, R-410A and R-12, among others.
They are used with chlorine-free HFC refrigeration systems, because they provide enhanced stability and lubrication and are more miscible than mineral oils and other synthetics with HFC refrigerants.
Key characteristics of POE oils
POE oils have high chemical and thermal stability and offer excellent wear protection and lubricity. They are powerful solvents, which helps them clean systems, but they also loosen debris that sometimes clogs systems. While they absorb water, they also react to it, forming sludge.
Applications
PAG oils are most frequently used in high-performance industrial refrigeration and cooling applications and automotive air conditioning systems. They are formulated to mix effectively with modern refrigerants for efficient oil circulation.
POE refrigeration oils are primarily used in modern air conditioning and refrigeration systems using HFC and HFO refrigerants. They are also used in hybrid and electric vehicles air condition systems and in retrofitting older HCFC systems to meet HFC standards.
Storage
Both PAG and POE lubricants attract moisture, which means extreme care is required when storing them to maintain lubricant integrity. They must be stored indoors, in a cool, dry environment inside tightly sealed original containers in a horizontal position.
Moisture tolerance
PAG and POE refrigeration oils are both hygroscopic, meaning they absorb water. PAG behaves like a sponge, drawing water from the air quickly; however, it locks it in, stopping it from reacting with system parts.
POE oils absorb less water, but ingress is more dangerous to equipment, as hydrolysis can occur, resulting in acid and sludge formation that damages compressors.
Compatibility
PAG lubricants have limited compatibility with other lubricants. They are incompatible with both PAO oils and mineral oils.
When combined, they create sludge or separation. Their high moisture absorption rate also makes them unsuitable to lubricate components like compressor shaft seals, O-ring and refrigerant line joints. They are, however, compatible with R134a and R1234yf refrigerants.
While incompatible with PAG oils, POE oils are compatible with mineral oils, common elastomers and plastics.
Electrical conductivity
PAG oils are classed as electrically conductive compared to both insulating mineral oils and POE oils. Their ability to absorb water and high polarity make them unfit for use in most high-voltage electric vehicle compressors, where high-dielectric-strength and non-conductive oils are necessary.
POE oils employed in refrigeration and electric vehicle compressors are engineered to act as high-performance electrical insulators and exhibit electrical conductivity near zero.
Stability
PAG oils typically exhibit superior thermal and chemical stability compared to POE oils in refrigeration systems, especially regarding resistance levels to moisture-induced equipment failure and high-temperature operations.
Although both are synthetic solutions, PAG is generally the preferred option for automotive air conditioning systems due to its enhanced stability, while POE oils are more widely used in commercial and residential heating ventilation and air conditioning systems. This is due to their less hygroscopic formulation and improved electrical insulating properties.
Whether you require PAG or POE refrigeration compressor lubricant, you can browse our product listings that include solutions from CPI Fluid Engineering and its Emkarate line.
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