Four additives, one job: make thick cannabis oil behave in hardware that wants a specific consistency. They also stretch volume, which is the part nobody advertises. Leaving them out costs more and leaves more room for cannabis.
A note from the fill line: the familiarity in that third column is exactly what makes these agents persuasive and exactly what makes them worth examining. Being common in a shampoo tells you nothing about being heated to vapor.
Propylene glycol
A synthetic diluent, thin and close to odorless, used as a solvent and humectant. In a cart it drops viscosity quickly, which makes it efficient at very small proportions and a favorite for that reason.
It carries flavor well, so it also serves as a vehicle for added terpenes. You'll meet it in food additives, cosmetics and pharmaceutical preparations, and it's a mainstay of nicotine vaping formulations, which is where much of the cart-era practice was borrowed from. That borrowing is worth noting on its own. Cannabis oil and nicotine liquid have very different natural viscosities, so a formulation approach designed for one arrived in the other without much re-examination.
Vegetable glycerin
A thick, faintly sweet liquid made from plant oils. Where propylene glycol thins, vegetable glycerin adds body and produces noticeably more visible vapor, which is why the two are often used together in a ratio.
The vapor volume is the point. A cart cut with it looks more productive than it is, and the sweetness can round off a flavor in a way some people find pleasant. It's common in food, cosmetics and pharmaceuticals, and it's the additive most responsible for the look of a big cloud. Cloud size is a poor proxy for anything. A larger visible plume mostly reflects how much glycerin is present rather than how much cannabinoid you received, which is why judging a cart by its exhale is judging the additive.
Polyethylene glycol
A polymer that comes in a range of molecular weights, used as a carrier and a thinning agent. PEG 400 is the grade most associated with vape formulation, chosen because it's effective at keeping thick oil mobile.
Outside cannabis it's routine in pharmaceutical preparations and personal care products, and in medicine it's a familiar excipient. Of the four it's the one that has drawn the most formulation scrutiny in vaping contexts, and it's also the one you're least likely to see named on a package. Molecular weight matters here in a way it doesn't for the others. PEG is a family rather than a single compound, so two products listing the same three letters can contain materially different substances.
MCT oil
Medium-chain triglycerides, a fraction of coconut or palm oil, used as a carrier rather than a thinner in the strict sense. It's the additive that most often gets marketed as the natural option, because it comes from a plant and sits on supplement shelves.
That framing is the thing to watch. Plant-derived and food-grade are accurate descriptions and neither one speaks to inhalation. MCT is an oil, and oils behave differently in a lung than they do in a stomach, which is the whole subject of the next section. The naturalness framing does real persuasive work, and it's the reason MCT persisted in the category longer than some of the others.
Safe to eat is not the same as safe to inhale
This is the single most important idea on the page, and it's routinely elided in marketing copy.
The safety record behind all four agents comes from ingestion, topical application and, in some cases, injection as a pharmaceutical excipient. Those are well-studied routes with decades of data. Inhalation is a different route, and a compound's behavior doesn't transfer between them.
Two things change. The first is the destination: inhaled material reaches lung tissue directly rather than passing through digestion, so it skips the processing that handles most of what we consume. The second is heat. A coil takes these compounds well past the temperatures they meet in food, and heating can change a molecule into something other than what was added.
We're deliberately stopping short of a health claim here, because the honest position is that inhalation data for these agents is thinner than their food-safety record and we're not in a position to close that gap. Saying so costs us nothing and it's the accurate position. A brand that claims certainty in either direction on this is telling you about their marketing rather than the literature. What we can say is what we do: none of the four goes into our oil, and the aroma comes from cannabis-native terpenes rather than a carrier system.
Put bluntly: when a brand answers a question about additives by citing food-grade status, they've answered a question you didn't ask.
Why are they used at all?
Two reasons, and only one gets discussed.
The stated reason is engineering. Cannabis oil is thick, ceramic hardware wants a specific viscosity range to wick properly, and a thinning agent moves the oil into that range cheaply. That's a real problem with a real solution.
The unstated reason is volume. An additive occupies space that cannabis would otherwise occupy, at a fraction of the cost, and the cart still looks and draws correctly. The two reasons are hard to separate from the outside, which is why the proportion matters more than the presence.
The alternative is matching hardware to oil rather than oil to hardware. It costs more and it's the route we take, which is why our carts run undiluted oil in ceramic built for it. It also constrains what we can offer. Undiluted oil narrows the hardware that will work, so the pairing gets decided early in development rather than at the filling stage.
How can you tell if they're in there?
Ask, mostly. This is the part where the paperwork can't help you as much as you'd like.
A California compliance panel tests seven categories: cannabinoids, residual solvents, heavy metals, pesticides, microbial impurities, mycotoxins and foreign material. Cutting agents are none of those things, so a routine certificate of analysis has no line for them. Across our own library of 502 documents, not one mentions any of the four, and that's expected rather than reassuring.
So the workflow is a question plus a price check. Ask the brand what's in the oil besides cannabis and terpenes. Then notice whether the price makes sense, because cannabis sets a floor on what a cart costs to produce and a cart well below it is telling you something about its contents.
