A Beginner’s Guide to Understanding E-Liquid
Technical Review: This article was originally published in 15.12.2023 and was fully updated in February 2026 to reflect current technical terminology and Irish regulatory context.
E-liquid (sometimes called “vape liquid”) is the consumable fluid used in refillable vaping devices. It is formulated to be heated by a coil, producing an aerosol that carries flavour and, where applicable, nicotine. This guide explains e-liquid in technical terms: what it is, what it contains, how ratios behave in devices, and how Irish rules shape what you can buy.
Definition
E-liquid is a mixture of propylene glycol (PG), vegetable glycerin (VG), flavouring components, and optionally nicotine, designed to be vaporised by a heating coil in a refillable vaping device.
Key Takeaways
- PG and VG control viscosity, wicking behaviour, and perceived throat sensation.
- Nicotine strength is labelled as mg/ml (concentration), not “how much you absorb”.
- Device type (MTL vs DTL) affects which ratios and nicotine ranges are typically used.
- In Ireland, product formats are shaped by EU TPD limits and the E-Liquid Products Tax (EPT).
- Most “bad taste” issues are maintenance or configuration problems, not mysterious liquid defects.
What E-Liquid Is Used For in a Device
Inside a tank or pod, e-liquid is drawn into a wick (usually cotton). The coil heats the saturated wick and liquid film, creating an inhalable aerosol. Performance depends on stable wicking, correct power, and a liquid viscosity that matches the coil design.
What’s in E-Liquid
Propylene Glycol (PG)
- Role: carrier for flavour components; lowers viscosity for faster wicking.
- Typical behaviour: clearer flavour definition and a more noticeable throat sensation in restricted airflow devices.
Vegetable Glycerin (VG)
- Role: increases viscosity; supports denser aerosol output.
- Typical behaviour: smoother feel and heavier vapour density, but requires stronger wicking/coil geometry.
Flavouring Components
Flavour is built from multi-component concentrates. Some profiles (especially cooling agents and strong sweeteners) can leave more residue on coil surfaces, which may reduce coil lifespan and affect flavour clarity over time.
Nicotine (Optional)
Nicotine strength is labelled as mg/ml. This is a concentration value. Actual delivery varies by device efficiency, airflow, coil temperature, and user behaviour. Avoid “cigarette-equivalent” charts: they are not technically reliable across devices.
PG/VG Ratios and How They Behave
| Common Ratio | Viscosity | Typical Device Match | Practical Notes |
|---|---|---|---|
| 50/50 | Medium | MTL pods and MTL tanks | Stable wicking in small ports; consistent flavour clarity |
| 60/40 | Medium–High | MTL/RDL crossover setups | Good balance where coils can handle slightly thicker liquids |
| 70/30 (VG/PG) | High | DTL sub-ohm systems | Requires robust wicking; allow longer saturation time on new coils |
Nicotine Strength: Labelling Basics
Nicotine strength is printed as mg/ml. A 10 ml bottle at 20 mg/ml contains 200 mg total nicotine (20 mg × 10 ml). Concentration and total content are not the same concept, but both matter for accurate interpretation of labels.
Shortfills and Nicotine Shots (Format Explanation)
In Ireland and the wider EU market, you will commonly see nicotine-free larger bottles (“shortfills”) designed to be combined with separate nicotine shots where permitted. The final concentration depends on dilution volume. A quick approximation for a single 10 ml shot is shown below:
| Example Mix | Assumption | Approx. Final Strength | Why It Matters |
|---|---|---|---|
| 10 ml shot (20 mg/ml) + 50 ml shortfill (0 mg) | Final volume ≈ 60 ml | ≈ 3.3 mg/ml | Common low-strength target for higher airflow setups |
| 10 ml shot (20 mg/ml) + 100 ml shortfill (0 mg) | Final volume ≈ 110 ml | ≈ 1.8 mg/ml | Lower concentration due to greater dilution |
Storage, Oxidation and Colour Changes
Nicotine is photochemically sensitive. Exposure to oxygen and UV light can accelerate oxidation, often visible as gradual darkening (clear to amber). Oxidation may also introduce pepper-like sensory notes and change flavour clarity. Store liquids sealed, away from direct light, at stable room temperature (commonly below 25°C) to reduce degradation of nicotine and complex flavour components.
Ireland-Specific Context: TPD Limits and E-Liquid Products Tax
In Ireland, nicotine products are regulated under the EU Tobacco Products Directive framework implemented in Irish law, including requirements such as maximum nicotine concentration and packaging constraints. In addition, Ireland introduced the E-Liquid Products Tax (EPT) with effect from 1 November 2025. EPT applies to both nicotine-containing and non-nicotine e-liquids at a flat rate per millilitre. This affects market pricing and how products are supplied in the State.
Nicotine-containing products are intended for adults aged 18+ only.
Common Setup Problems (Technical, Not Medical)
Burnt Taste on First Use
- Likely cause: coil not fully saturated.
- Technical fix: prime the coil, fill, then wait longer for higher-VG liquids before first activation.
Leaking or Gurgling
- Likely cause: overfilling, worn seals, incorrect viscosity for the coil, or condensation.
- Technical fix: check O-rings, avoid overfilling, ensure the ratio suits the coil design.
Weak Flavour After Changing Liquid
- Likely cause: flavour ghosting from residue in cotton/metal surfaces.
- Technical fix: rinse and dry tank parts; replace pods with integrated coils when switching strong profiles.
FAQ
What does “mg/ml” nicotine strength mean?
It is the concentration of nicotine in the liquid: milligrams of nicotine per millilitre of e-liquid. It does not directly describe how much nicotine is absorbed in use, which varies by device configuration and behaviour.
Why has my e-liquid turned darker over time?
Darkening is commonly associated with oxidation (exposure to oxygen and light) and, in some flavours, coil-related residue. It is a stability and storage issue rather than a sign of “more nicotine”.
Does higher VG always mean better performance?
No. Higher VG increases viscosity and vapour density potential, but it also demands stronger wicking and suitable coil geometry. Many pod systems perform best with balanced ratios such as 50/50.
Intent Disclosure
This article provides technical, educational information about e-liquid composition and regulated product formats in Ireland. It does not provide medical, safety, or cessation advice.
Last Updated: February 2026
