Argon vs. Krypton Gas Fill: Does It Matter?

Modern insulated windows are filled with inert gas rather than air. According to Lawrence Berkeley National Laboratory, these gases improve insulation—but which one is better?

How Gas Fill Works

According to the U.S. Department of Energy, gas fills improve window performance by:

1. Lower conductivity: Heavier gas molecules transfer heat more slowly
2. Reduced convection: Denser gas has less convection current
3. Inert properties: Won't degrade coatings or react with materials

The Options

According to NFRC and LBNL:

| Gas | Thermal Conductivity | Cost | Optimal Gap Width |
|-----|---------------------|------|-------------------|
| Air | Baseline | Free | 1/2" |
| Argon | 34% lower | Low | 1/2" |
| Krypton | 63% lower | High | 3/8" or less |

Performance Impact

According to LBNL testing:

| Configuration | U-Factor |
|---------------|----------|
| Double Low-E, air fill | 0.32 |
| Double Low-E, argon fill | 0.27 |
| Double Low-E, krypton fill | 0.24 |

Argon improves U-factor by about 15% over air. Krypton improves another 10% over argon.

When Argon Makes Sense

According to DOE, argon is the standard choice because:

• **Excellent value:** Adds only $20-40 per window
• **Good performance:** Significant improvement over air
• **Widely available:** Standard in quality windows
• **Works with standard gap:** 1/2" spacing common in double-pane

When Krypton Makes Sense

According to LBNL, krypton is worth considering when:

• **Triple-pane windows:** Narrower gaps benefit from krypton
• **Thin-profile triple-pane:** Same thickness as double-pane
• **Maximum efficiency required:** Passive house or similar standards
• **Budget allows:** Adds $75-150 per window

Does Gas Leak Out?

According to FGIA research, quality IGUs lose about 1% of gas per year. According to DOE, windows retain effectiveness even with partial gas loss—they never become worse than air-filled.

After 20 years, a window initially filled with 90% argon might have 70% argon—still providing meaningful benefit.

The Bottom Line

For most residential applications, argon is the clear choice—excellent performance at minimal cost. Krypton makes sense for triple-pane or when maximum performance justifies the premium.

*For complete glass options, see: [Single, Double, and Triple-Pane Windows](/guides/single-double-triple-pane-windows)*