Many suppliers of e-juice, including Slim's, offer a range of customization for base fluid. As a consumer, the project is finding out what proportions of these carrier ingredients will give you the most satisfying and functional vape experience. In choosing a mix to best suit your preferences and/or sensitivities--as well as the personal vaporizer (PV) equipment you are using--it helps to know a bit about the components.
Typically, base fluid--that is, unflavored e-juice--is made-up primarily of a combination of propylene glycol (PG) and vegetable glycerin (VG). The partnership of these two ingredients is essentially what creates the medium for both nicotine and the flavorings that make e-juice so tasty. With minimal knowledge and a little experience, you will soon start to get a sense of the type of vape experience different base ingredient ratios will give you. As the proportions of PG to VG in any particular e-juice may vary, let's take a brief look at some properties of each.
PG is is in the U. S. Food and Drug Administration's GRAS category (i.e., "generally recognized as safe") and is a commonly used stabilizing food additive. It is a frequent ingredient in ice cream, cake mixes, margarine, and soda, among others.
Both PG and VG are flavor carriers, but in this regard PG is superior. PG also has a great throat hit, reminiscent of tobacco smoke, which is one reason a percentage ratio of up to 80/20 PG/VG is often favored by new vapers who may still be feeling the pangs of their parting from cancer sticks. Something to keep in mind with PG is that it can be more drying to the mucous membranes, when vaped, than VG. Some people will naturally be more sensitive to this than to others, and taking plenty of fluids should offset any such effects. If you find that despite drinking water, you continue to experience dryness or persistent throat irritation with PG, you may be one of a very few people who have an allergic-type reaction to it, and should switch to exclusively VG based e-juice.
VG is made from --yes, you guessed it, vegetables! It is frequently a by-product of biodiesel manufacture. Sounds a little scary, I know--but in fact, glycerin is an organic compound widely used as a humectant and preservative in many common products meant for personal consumption, including medicines, make-up, toothpaste, and food. VG is also approved by the FDA for consumption.
VG is cherished by vapers who value the "cloud factor" in vaping--it makes huge amounts of vapor! Although it contains no sugar, VG also imparts a sweet taste on the tongue and gives a wonderfully smooth throat hit. In its liquid form, however, it is considerably thicker than PG, and will tend to gunk-up atomizers more quickly, which, in turn, means more frequent cleaning and/or replacing of the coil unit you are using. In the case of extreme (80-100%) VG based e-juices, using a more advanced personal vaporizer, such as a rebuildable atomizer (RBA), or a dripping atomizer (RDA) is recommended. When used in tanks or cartomizers, very high percentage VG juices can result in the dreaded "dry hits"--these deliver an unpleasant taste and occur when the wicking material in your tank is unable to absorb the viscous fluid quickly enough to deliver it to your heating element.
Knowing the basics covered in this article will help you make a better choice for yourself, and I would encourage beginners to stick with a moderate blend at first: half and half is a fine place to start. But there really is no "right answer" here--and by the same token, it's nice to know that you mostly can't go wrong.
Whether you end up opting for a PG-heavy or VG-heavy blend, 50/50, or prefer to vape exclusively one or the other, your choice ultimately comes down to a personal decision about what aspects of the vaping experience you value most and want to emphasize. You may have to play around a bit with proportions before you find your ideal base ratio. Or you may find, as so many do, that your tastes, and therefore your requirements of a base, will change, depending on your physical vaping style, the flavor of a particular e-juice, your mod--even your mood. Vaping is meant to be fun.
Relax and enjoy the process, and, as always, breathe!
--Nom de Plume