Walking into a flavour shop for the first time, one notices the shelves lined with sleek bottles promising everything from icy menthol to ripe mango. Yet the most important variable on that label is often invisible: the ratio of propylene glycol (PG) to vegetable glycerin (VG). This ratio is not a marketing gimmick; it is the primary engineering control for what users call “throat hit”—the sharp, satisfying sensation at the back of the throat that mimics the feel of smoking.
The distinction between a smooth, almost silky vapor and a harsh, rasping draw is almost entirely a function of PG concentration. To understand why flavour shops so precisely calibrate this ratio, we must first examine the physical and chemical properties of PG itself.
The Chemistry Behind the Sensation
Why PG Creates Throat Irritation
Propylene glycol is a small-molecule diol with a low viscosity and high hygroscopicity—it readily absorbs moisture from its surroundings. When vaporized and inhaled, PG particles rapidly strip water from the mucous membranes lining the throat and upper airway. This localized dehydration triggers the same nerve endings that respond to physical irritants, generating a sharp, scratchy sensation that users experience as throat hit.
The effect is not merely subjective. Studies on occupational exposure to propylene glycol mist have documented transient throat irritation at concentrations above 300 mg/m³—levels well within the range produced by a typical vaping device. Flavour shops exploit this known irritant property to replicate the “kick” that former smokers expect from tobacco.
VG’s Counterbalancing Role
Vegetable glycerin, by contrast, is a larger, more viscous molecule that forms heavier droplets. It coats the throat rather than dehydrating it, producing a smooth, almost creamy vapor with minimal irritation. A high-VG blend (e.g., 70% VG to 30% PG) is the standard for “cloud chasing” because it generates dense vapor plumes, but it sacrifices the sharpness that many users find essential for satisfaction.
The tension between these two compounds is where every flavour shop’s craft resides. Too much PG, and the throat hit becomes painful; too little, and the experience feels hollow, like breathing steam from a humidifier. The ratio is a tuning dial for sensation.
Practical Ratios in the Flavour Shop
The Classic 50/50 Standard
For decades, the 50% PG / 50% VG blend has been the default for starter kits and pod systems. This ratio provides a moderate throat hit that is firm enough to satisfy a smoker converting to vaping, yet smooth enough to avoid choking. Flavour shops often recommend this ratio for first-time buyers because it balances three competing demands: throat sensation, flavor delivery, and device compatibility.
PG is also the superior flavor carrier. Many flavor concentrates are dissolved in PG, so a 50/50 blend ensures the aromatic molecules reach the taste buds efficiently. A customer who tries a premium tobacco flavor in a high-VG blend may complain it tastes “flat”—the shop knows the PG ratio is the culprit.
High-PG Blends for Mouth-to-Lung Users
Mouth-to-lung (MTL) vaping mimics the draw of a cigarette: the user pulls vapor into the mouth first, then inhales. This technique demands a higher PG ratio, typically 60% to 70%, to generate the tight draw and pronounced throat hit that replicates a combustible cigarette. Flavour shops catering to ex-smokers often stock dedicated MTL liquids at 65% PG.
I once observed a veteran flavour shop owner troubleshoot a customer’s complaint that a “bold” 36 mg/mL nicotine salt liquid felt like “nothing.” The owner swapped the bottle for the exact same flavor but at 70% PG instead of 50%. The customer’s reaction was immediate: “That’s it. That’s what I was missing.” The nicotine concentration hadn’t changed—only the ratio had.
Low-PG Blends for Direct-to-Lung Devices
Direct-to-lung (DTL) vaping involves inhaling the vapor directly into the lungs, a style that favors high-VG blends (70% to 80%) for their smoothness and cloud production. However, even among DTL users, there is a subpopulation that finds pure VG too “wet” or lacking in sensation. Many premium flavour shops now offer “hybrid” lines—e.g., 40% PG / 60% VG—that preserve a whisper of throat hit without overpowering the user.
The Science of Nicotine and PG Synergy
How Salt Nicotine Changes the Equation
Nicotine itself is a throat irritant, and its effect is additive with PG. Freebase nicotine, the traditional form, is alkaline (pH ~8-9) and produces a harsh throat hit even at moderate concentrations. Nicotine salts, by contrast, are formulated with benzoic acid to lower the pH to roughly 5-6, making the vapor much smoother at higher nicotine levels.
Flavour shops use this chemistry to manipulate throat hit without changing the PG ratio. A 50 mg/mL salt nicotine liquid at 50/50 PG/VG will feel milder than a 12 mg/mL freebase liquid at the same ratio. The shop’s job is to calibrate both variables—ratio and nicotine form—to hit the user’s preferred sensation sweet spot.
The Temperature Factor
Device wattage also interacts with PG ratios. Higher temperatures vaporize PG more efficiently, increasing its concentration in the aerosol. A 50/50 blend used in a sub-ohm tank at 80 watts will feel harsher than the same liquid in a low-wattage pod system. Experienced flavour shops often recommend lowering the PG ratio by 10% when customers upgrade to higher-power devices, anticipating the temperature effect.
This is why many shops now print “best at 30-50W” on their bottles. It’s not just a safety note—it’s a throat-hit calibration guide.
A Forward-Looking Note on Precision
The future of flavour shops lies in hyper-personalization. We are already seeing custom blend stations where customers specify their exact PG/VG ratio, nicotine strength, and flavor profile. Some shops use refractometers to measure the viscosity of the final blend, ensuring that each bottle matches the customer’s preferred throat hit within 2%.
As the industry matures, the question will shift from “What ratio do you want?” to “What sensation are you trying to replicate?” The PG ratio is not a technical detail—it is the language through which a flavour shop translates a former smoker’s memory of a cigarette into a safe, satisfying vapor. The next time you pick up a bottle, ask for the PG percentage first. The flavor is the destination, but the ratio is the road.