Vegetable Glycerin referred to as VG is one of the main ingredients in the production of E-Liquid. It makes up part of the liquid that heats up to create the vapour that is produced. VG is also the ingredient that contributes to Vapour Production. It is possible to make E-Liquid with 100% VG which will generally give loads of vapour, but not much 'Throat Hit'. People use 100% VG to make the final e-liquid slightly sweeter tasting, and also approx. 1 in 1000 people have an intolerance to PG. VG is also Kosher. Most E-Liquids contain 70%-80% PG and 20-30% VG mix, but there is no hard and fast rule as to the ratios you use.