Vegetable glycerin (VG) will increase vapor production and Propylene Glycol (PG) will increase flavor and throat hit. Some people are allergic or sensitive to PG and will get tightness in the chest or itchy throat. Most juice companies have a set ratio for their flavors but other sites let you choose the pg/vg ratio. It is all about finding that "sweet spot" for you juices, I have settled at a 50/50 ratio at 12mg nic.