Polyol ester oils are used in the compressors of refrigerating systems using R-134a or R-12 as refrigerant. They are also used to lubricate parts in jet engines.
Polyol ester oil is a class of synthetic oils with the ability to both flow freely at low temperatures and not be degraded by high temperatures. They can be used without change for several years.
Polyol ester oils are often used as a replacement for mineral oils when replacing chlorine-based refrigerants with non-chlorine alternatives. They are excellent solvents and can dissolve contamination left by the mineral oil without losing functionality. One undesirable property of polyol ester oils is a tendency to absorb humidity.