It's my feeble understanding that Humco brand is a "synthetic" glycerol,
but have not an idea how/what it's made from. If the label doesn't say
99.8% pure USP vegetable glycerin, it could also be made from animal fats. Some people have problems with VG, it may have something to do with the questionable ingredients. Pure VG is made
through a very complex process, can be "aqueous" as in ECOpure VG, meaning that it has not distilled all the excess moisture away, or distilled VG, little thicker and sweeter. The only way you'd know is to see it side by side.
Hope this helps answer your question. Any drugstore or even Walmart will have pure VG, may have to ask for it, even some grocers have it in the baking section.