Hygroscopic means affinity for moisture, although some (even experts) use <hydroscopic>, incorrectly.
Agroscopic = an affinity for farm produce?
Just joking around.
The hygroscopic oils hold moisture that creates some pretty interesting acids that can lead to pinholes in the evaporator (think of the dreaded 140 evap.).
#1 cause of compressor failure according to one article in a MACS? publication is lack of oil.