VG/PG Ratio & Temperature Behaviour in Ireland
How VG and PG React to Temperature, Humidity and Pressure Conditions
This technical document explains how vegetable glycerin (VG) and propylene glycol (PG) behave under varying temperature and humidity conditions, with specific reference to Irish climate patterns. It focuses on viscosity, hygroscopic behaviour, atmospheric pressure influence, and wicking dynamics in regulated devices.
Technical Definition
VG (Vegetable Glycerin) is a high-viscosity, hygroscopic liquid responsible for vapour density. PG (Propylene Glycol) is a lower-viscosity carrier fluid that enhances flavour transmission and capillary wicking speed.
Viscosity–Temperature Dependence
Liquid viscosity increases as temperature decreases. In Ireland, where winter temperatures commonly range between 0–8°C, high-VG formulations may thicken significantly compared to indoor room temperature (~20°C).
| VG/PG Ratio | Room Temp (~20°C) | Cold Temp (~5°C) | Wicking Behaviour | Device Pairing |
|---|---|---|---|---|
| 50/50 | Low–moderate viscosity | Slight thickening | Fast capillary absorption | MTL / pod systems |
| 60/40 | Moderate viscosity | Noticeable thickening | Balanced absorption | General regulated devices |
| 70/30 | High viscosity | Significant thickening | Slower saturation at low temp | Lower-resistance coils (see: Coil Materials & Resistance Explained) |
Hygroscopic Behaviour (Ireland Humidity Context)
VG is highly hygroscopic, meaning it absorbs moisture from the surrounding air. In Ireland’s high-humidity environment, improperly sealed bottles may absorb atmospheric moisture over time.
This can slightly reduce viscosity and may contribute to increased condensation, spitting, or minor leakage in certain tank systems.
Pressure Differential & Suction Dynamics
Capillary wicking is assisted by negative pressure (suction) generated during inhalation. In colder conditions, thicker liquid requires greater pressure differential to overcome flow resistance within cotton channels.
Stronger inhalation may temporarily compensate for increased viscosity, assisting liquid movement toward the heating element.
Rapid atmospheric pressure changes — common in Irish weather systems — may also affect internal tank pressure balance and seal stability, occasionally contributing to leakage behaviour.
Viscosity vs Temperature – Conceptual Behaviour Curve
20°C | Normal flow
10°C | Noticeable thickening
5°C | Reduced capillary speed
0°C | Delayed saturation risk
Thermal Compensation During Operation
When coil temperature increases during activation, liquid viscosity decreases locally near the heating element. This partially offsets cold-weather thickening during sustained use.
Technical Recommendations (Ireland Climate)
- Allow devices stored outdoors to reach room temperature before activation.
- Prime coils longer in winter conditions.
- Use balanced VG/PG ratios (50/50 or 60/40) in compact pod systems during colder months.
- Monitor for condensation buildup in high-humidity environments.
FAQ – VG/PG & Climate Behaviour
Ireland Notice (18+)
Technical documentation for adult users (18+) in Ireland. No medical or cessation claims are made.