The other main base liquid is vegetable glycerine, which also has no scent or colour, but is much thicker and sweeter than PG. It comes from plants and doesn't have any toxic effects, meaning it's often used in medicines and burn remedies. You'll also find it in lip gloss and soap, as well as other products that need to be delivered orally via capsules or lotions that are rubbed into the skin. It can work effectively in any of these forms.
VG is gentler on the throat than PG and can create larger, denser clouds.