Two numbers separated by a slash appear on every bottle of e-liquid sold through legitimate retailers in Ireland: the PG/VG ratio. For experienced vapers these numbers are second nature, immediately communicating whether a liquid is suited to their device and what kind of experience it will produce. For newer vapers and those who have never had the ratio properly explained, they remain a confusing feature of a product label whose significance is not intuitively obvious.
Understanding the PG/VG ratio is not optional knowledge for anyone who wants to get the best possible experience from their device. Using a liquid with the wrong ratio for your coil is one of the most common causes of the complaints that drive new vapers away from the category: dry hits that taste burnt, flooded coils that gurgle and spit, and flavour that seems muted or wrong. Getting the ratio right, by contrast, produces the clean flavour and consistent performance that makes vaping genuinely satisfying.
What Propylene Glycol Is and What It Does
Propylene glycol — PG — is a synthetic organic compound classified as generally recognised as safe (GRAS) by food regulatory authorities globally and used extensively in food processing, pharmaceuticals, and cosmetics. It is a thin, colourless, essentially odourless liquid with a faintly sweet taste and a remarkable ability to carry and distribute flavour compounds evenly through a mixture.
In e-liquid, PG serves as a flavour carrier, a throat hit producer, and a wicking aid. As a flavour carrier it is excellent: PG molecules effectively surround and transport the complex flavour compounds in concentrate mixtures, distributing them evenly through the finished liquid and releasing them efficiently when the coil vaporises the liquid. This is why high-PG liquids tend to produce cleaner, more accurate flavour reproduction — the PG is doing its job as a flavour vehicle effectively.
The throat hit associated with PG is a direct pharmacological effect of the compound at the concentrations used in e-liquid. PG vapour creates a mild stimulant effect at the back of the throat that many former smokers find familiar and satisfying. It partially replicates the sensation of a cigarette drag, which is why early e-liquids were heavily PG-based and why many MTL users and ex-smokers prefer liquids with meaningful PG content.
PG is also relatively thin, with a viscosity closer to water than oil. This low viscosity is critical for wicking: the liquid must flow from the tank through the cotton wicking material to the coil surface quickly enough to replace what is being vaporised. Thin liquids flow faster through fine cotton and are less likely to cause the dry hits that result from the coil surface running out of liquid mid-draw.
What Vegetable Glycerin Is and What It Does
Vegetable glycerin — VG — is a natural compound derived from plant oils, typically soybean, coconut, or palm oil. It is a thick, viscous liquid with a pronounced natural sweetness and an extraordinary ability to produce vapour. When heated at vaping temperatures, VG produces the dense, voluminous aerosol clouds that are the defining visual characteristic of sub-ohm vaping and cloud-focused devices.
The vapour production advantage of VG is substantial. At equivalent temperature and wattage, a high-VG liquid produces significantly more visible vapour than a high-PG equivalent. This is because VG produces denser aerosol particles that scatter light more effectively, creating the thick, visible clouds associated with sub-ohm setups. For vapers who value vapour production as part of the aesthetic experience, VG percentage is one of the most important specifications.
VG is also notably smooth on the throat. Where PG produces a perceptible throat hit, VG is almost entirely smooth, and high-VG liquids at equivalent nicotine concentrations to high-PG liquids produce a substantially gentler inhale. This smoothness makes high-VG liquids comfortable at higher wattages and during extended sub-ohm sessions where the cumulative throat exposure from many draws would otherwise become uncomfortable.
The significant limitation of VG is its viscosity. VG is substantially thicker than PG — its viscosity is comparable to a light oil. This thickness creates wicking challenges in devices with fine cotton channels. The cotton in MTL coils and many pod systems has narrow wicking ports designed to flow relatively thin liquid efficiently; high-VG liquids move through these channels too slowly to keep pace with the vaporisation rate during active drawing, causing the cotton to run dry before it can be replenished. The result is a dry hit — a harsh, unpleasant, often burnt-tasting draw that also damages the cotton and shortens coil life.
How Different Ratios Change the Experience
The PG/VG ratio is expressed as two percentages — PG first, VG second — and the proportional shift between these two compounds produces predictable and consistent changes to the vaping experience. Understanding these changes allows you to select a liquid matched to your preferences.
High-PG liquids (sixty percent PG and above) are thin, fast-wicking, throat-hit-forward, and flavour-clear. They are the appropriate choice for MTL devices, tight pod systems, and users who prioritise the cigarette-like throat hit or maximum flavour accuracy. The vapour production is modest — high-PG liquids do not produce dramatic clouds — and the flavour delivery is often described as clean and precise. Nicotine salts in high-PG or balanced formulations are the most common format for this end of the spectrum.
Balanced liquids (around fifty percent PG to fifty percent VG) are versatile across a wider range of devices than either extreme. They wick well in MTL coils, produce more vapour than pure-PG liquids, and deliver a softer throat hit than the high-PG end of the spectrum. Many vapers who use both a pod system and a sub-ohm device as their daily setup opt for a balanced fifty-fifty liquid that performs acceptably in both rather than maintaining separate liquids for each device.
High-VG liquids (seventy percent VG and above) are thick, cloud-producing, throat-smooth, and slightly sweet from the VG base. They are the standard choice for sub-ohm devices with mesh coils at twenty-five watts or above. The wide wicking ports of sub-ohm coil heads are specifically designed for these thick liquids, and the performance difference between a seventy-VG liquid and a fifty-fifty liquid in a well-matched sub-ohm device is immediately apparent in vapour density and flavour intensity. Shortfill liquids — the large-bottle zero-nicotine liquids designed to be combined with a nicotine shot — are almost universally high-VG formulations.
Device Compatibility: The Non-Negotiable Matching Rule
Device compatibility with PG/VG ratio is not a matter of preference — it is a physical constraint determined by the design of the coil’s wicking system. Using a high-VG liquid in an MTL device is guaranteed to cause wicking problems regardless of how good the liquid is or how well the device was designed. The cotton channels simply cannot move thick liquid fast enough to maintain adequate saturation during use.
The wicking problem manifests as dry hits — draws where the coil surface has run dry and the heat sears the cotton directly rather than vaporising liquid. Dry hits taste characteristically harsh and burnt, are unpleasant to inhale, and damage the cotton fibres, shortening the coil life significantly. A coil that might last two weeks with appropriate liquid may fail within days if consistently used with a too-thick liquid.
The reverse problem — using a thin, high-PG liquid in a sub-ohm device designed for high-VG — is less likely to cause immediate damage but produces an inferior experience. The device produces less vapour than its design intends, the flavour is typically less rich than it would be with an appropriate high-VG liquid, and in some coil designs the thinner liquid can flood the coil slightly, producing a gurgling draw.
The practical rule: check your device’s recommended liquid viscosity before purchasing e-liquid. Reputable coil head manufacturers publish recommended PG/VG ratios on their packaging or product listings. Pod systems and MTL devices typically specify a minimum PG content of forty percent and a maximum VG of sixty percent. Sub-ohm tanks at twenty-five watts or above typically work best with seventy percent VG or higher. Following these guidelines from the outset saves the frustration of poor coil performance and wasted liquid.
Steeping and How Ratio Affects Flavour Development
The PG/VG ratio also affects how e-liquid flavour develops over time during steeping — the deliberate resting of freshly purchased or freshly made liquid. The viscosity of the base liquid influences how quickly the flavour concentrate molecules distribute through the liquid and how they interact with each other during the maturation process.
High-PG liquids tend to steep faster because the lower viscosity allows the flavour molecules to diffuse more easily throughout the liquid. Fresh high-PG fruit and menthol liquids often taste at or near their best immediately after purchase. High-VG liquids, particularly complex dessert and bakery profiles, may take longer to reach their optimal flavour because the thicker medium slows the diffusion of flavour compounds into a fully integrated blend. Shaking high-VG liquids vigorously before use helps distribute flavour molecules that may have settled or remained in locally high concentrations.
For vapers who buy premium complex liquids specifically for the flavour experience, storing them at appropriate conditions — cool, dark, with minimal headspace — and allowing a period of resting before tasting at optimal flavour is a practice that adds no cost and noticeably improves the experience for certain profile types. Trying the same liquid fresh from the bottle and again after two weeks of correct storage gives you a direct comparison that is more informative than any general guidance about steeping can be.
