An excerpt from thead linked in my signature below...
PG versus VG juices
PG is propylene glycol and VG is vegetable glycerin.
Either of these ingredients can be purchased relatively cheaply and easily by themselves.
They can be used for making your own liquid if desired. or for cutting
juice you have purchased.
As far as differences go, this is what I have gathered from reading things here and there.
1) VG is thicker (more viscous)
2) VG vaporizes at a lower temperature
3) VG produces better vapor
4) VG is somewhat sweeter
Because of the above...
1) VG does not wick quite as well
2) VG may gunk up your atomizer more quickly
3) VG produces a somewhat cooler vapor which may reduce throat hit