Argon Gas Fill Guide
Why argon, how it works, optimal cavity widths, depletion rates, and when to specify krypton for slim cavities. All CSU units are argon-filled at no extra charge.
Technical Guide
Air vs Argon vs Krypton
Argon is a colourless, odourless, non-toxic inert gas — 0.93% of Earth’s atmosphere. It has 34% lower thermal conductivity than air, improving DGU insulation by ~15%. CSU offers argon fill at 90%+ concentration as an optional upgrade on any unit.
| Property | Dry Air | Argon (Optional) | Krypton (Special) |
|---|---|---|---|
| Thermal Conductivity | 0.026 W/mK | 0.018 W/mK | 0.010 W/mK |
| Density | 1.23 kg/m³ | 1.66 kg/m³ | 3.43 kg/m³ |
| U-Value Benefit | Reference | ~15% better | ~25% better |
| Optimal Cavity | 12-16mm | 16-20mm | 10-12mm |
| Cost | POA | Optional upgrade | ~50× argon (premium) |
| Atmospheric % | 78% N₂ + 21% O₂ | 0.93% | 0.0001% |
| Depletion Rate | N/A | <1% per year | <1% per year |
| Safety | N/A | Inert, non-toxic, safe | Inert, non-toxic, safe |
When to Specify Krypton
- Heritage / slim-fit: 6-12mm cavities where argon is less effective
- Slim TGU: Where thinner profile is needed (28mm TGU with krypton matches 44mm with argon)
- Passivhaus: Where absolute maximum thermal performance is required
- Listed building frames: Where standard cavities won’t fit
Cavity Gas Fill
Air vs Argon vs Krypton — Heat Flow
Air
2.8 W/m²K
Argon
2.6 W/m²K
Krypton
2.4 W/m²K
Lower U-value = slower heat flow = better insulation. Denser gas fills slow both the heat-flow arrows and molecule movement shown above.
Centre-pane U-value, EN 673 calculation basis, 16mm cavity
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