Hygroscopic oil has a high affinity for water.

Hygroscopic oil has a high affinity towards water/moisture. At higher temperature, water content in the refrigeration oil and refrigerant reacts, forming acids which can damage the refrigeration system equipment. Synthetic oils, Polyalkylene glycol (PAG), and Polyolester (POE) are highly hygroscopic and readily absorb moisture/water. Greater care should be taken while handling these refrigeration oils so that very minimum exposure is made to the atmosphere.