Vegetable Glycerine and
Propylene Glycol
Both are used in various food, medicine and grooming products amongst other things. Some people don't jibe well with one or the other, though. Generally, PG juice produces better flavored vapor while VG is supposed to be more about heavier vapor production and throat hit but I do not find this to be exactly "written in stone". A really common mixture among vendors who don't allow you to choose at order is 80% PG and 20% VG but all kinds are out there including simply 100% of either one.
When it comes down to it, unless you know you are, say, allergic to VG you should just see what you prefer. You may very well find it doesn't much matter. I personally don't have a preference as yet but have only tried one pure VG and one pure PG juice so far.
To summarize, there are two main reasons why two "types" of juice exist: some people cannot ingest one of them and they are
technically supposed to each provide a different vaping experience.
Yeah I guess if you're allergic to both you're stuck on the stinkies! :/
