Argon is a colourless, odourless noble gas used as a filling between the panes of double and triple glazing. Argon conducts heat less efficiently than air, improving the insulation value of your windows. Virtually all modern high-performance and triple glazing is filled with argon.
Why argon?
Air consists of 78% nitrogen and 21% oxygen — these molecules move quickly and transfer heat. Argon molecules are heavier and slower, so less heat is transferred from inside to outside (or vice versa).
| Property | Air | Argon | Krypton |
|---|---|---|---|
| Thermal conductivity | 0.026 W/mK | 0.018 W/mK | 0.009 W/mK |
| Insulation improvement | Reference | ~30% better | ~50% better |
| Cost | Free | Minimal extra | Much more expensive |
| Use | Old double glazing | High-performance, triple | High-end triple glazing |
U-value and glazing types
| Glass type | Construction | U-value (approx.) |
|---|---|---|
| Single glazing | 1 pane | 5.8 W/m²K |
| Old double glazing | 2 panes + air | 2.8 W/m²K |
| Low-E double glazing | 2 panes + air + coating | 1.8 W/m²K |
| High-performance double | 2 panes + argon + coating | 1.1 W/m²K |
| Triple glazing | 3 panes + argon + coatings | 0.6-0.8 W/m²K |
The lower the U-value, the better the insulation.
How long does argon last in the glass?
- Well-manufactured double glazing loses about 1% argon per year
- After 20-25 years there’s still sufficient argon for good insulation
- If the edge seal (spacer) is damaged, it can leak faster — recognisable by condensation between the panes
Can argon be replaced?
No, you can’t refill argon. If there’s condensation between the panes, the entire glass unit needs replacing. The frame can usually stay in place.
Common mistakes
- Assuming all high-performance glass contains argon — Check the certificate or label on the spacer
- Ordering windows without argon to save money — The price difference is minimal (€5-10 per pane), the insulation difference is significant
- Ignoring condensation — Condensation between panes = broken seal = argon lost = poor insulation
Related terms
- Glazing
- Insulation value (R-value)
- Window frame
- Top-hung window