Argon fill (IGU)
Argon gas fills the cavity in an insulated glass unit. Lower conductivity than air cuts U-value 10-20%. Leaks ~1% per year; quality IGUs retain 80%+ at 20 years.
Ask Chalkline about this →Argon fill is argon gas used to fill the air gap between glass panes in an insulated glass unit (IGU, sometimes called a “double-glazed window”). Argon has a thermal conductivity of around 0.018 W/m·K, compared to 0.026 W/m·K for air, so substituting argon for the air in the cavity reduces heat conduction through the window cavity and lowers the IGU’s overall U-value by typically 10 to 20%. It is the default cavity-fill on volume-residential double-glazed windows in Australia (verified 2026-05-16).
How the fill is installed and contained:
- IGU manufactured by sealing two (or three, for triple glazing) glass panes around the perimeter with a spacer bar (commonly an aluminium or thermally improved spacer) and a primary sealant (commonly polyisobutylene or PIB) on the inner edge, plus a secondary sealant (commonly polysulphide or silicone) on the outer edge.
- Argon injected before the secondary sealant closes. The unit is gas-filled in the factory; you do not “top up” an IGU in service.
- Desiccant in the spacer bar absorbs any residual moisture, preventing internal fogging.
- The unit is shipped and installed with the argon retained at 90%+ concentration.
How argon leaks over service life:
- Argon migrates through the perimeter seal at typically 1% of the cavity volume per year.
- A 20-year-old IGU with intact seal would retain ~80% argon. Performance falls roughly linearly with concentration.
- A seal failure (visible fogging, broken outer seal) accelerates leak markedly.
- Once cavity concentration falls below ~50%, the argon advantage is mostly gone.
Builder takeaway:
- Specify argon fill on the energy-report-rated whole-window U-value. The IGU certificate gives you the as-manufactured argon concentration (commonly 90% or 92%).
- Specify a warranted gas-fill retention rate (commonly 10 years at 80%) for any IGU on a project where energy efficiency over the dwelling’s life matters.
- Inspect on delivery: a unit with a damaged perimeter seal at the corners is leaking argon now; reject the unit.
Argon vs other gas fills:
| Gas fill | Cost | Conductivity (W/m·K) | Typical use |
|---|---|---|---|
| Air | Free | 0.026 | Lowest-grade IGU |
| Argon | Modest | 0.018 | Volume-residential default |
| Krypton | High | 0.0095 | Premium, narrow-cavity assemblies (12 mm or less) |
| Xenon | Very high | 0.0055 | Specialty only, rarely seen |
Also known as: argon-filled IGU; argon double glazing; gas-filled double glazing.
Category: Materials.
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Last updated: 2026-05-16. Verified: 2026-05-16. Quarterly review for currency.