Argon, in almost every case. Krypton and xenon insulate better per millimetre but only in narrow cavities, and xenon is priced out of ordinary construction. The part that deserves your attention is not which gas was specified, it is whether the gas is still in the unit, and whether anyone can demonstrate it was ever there.
Gas filling is the most quietly oversold item in a glazing quotation. It is genuinely useful, the physics is real, and it is also invisible, unverifiable by eye, and the smallest of the levers available. That combination is worth understanding before you pay for it.
The Four Options
A sealed unit cavity contains either dry air or an inert gas. All the gases used are denser and less conductive than air, which slows both conduction and convection across the cavity.
| Fill | Relative insulation | Efficient cavity width | Cost | Where it belongs |
|---|---|---|---|---|
| Dry air | Baseline | 16 to 20mm | Included | Perfectly serviceable. Most of the benefit of double glazing comes from the cavity itself |
| Argon | Roughly 30% better than air | 16 to 20mm | Small premium | The sensible default for double glazing. Cheap, abundant, well understood |
| Krypton | Better than argon per millimetre | 6 to 9mm | Substantially higher | Narrow cavities, which in practice means triple glazing. Wasted in a wide cavity |
| Xenon | Best of the four | Narrow | Prohibitive | Effectively never specified in ordinary construction |
Two things in that table do most of the work. Argon delivers roughly a 30% improvement over air for a small cost, which is why it has become the default. And krypton, despite being the better gas, only outperforms argon in a narrow cavity, because that is the width at which its own convection behaviour is favourable.
Krypton specified into a wide cavity. It is the more expensive gas, so it reads like the premium choice on a quotation, but in a 16mm or 20mm gap it does not deliver its advantage. Krypton belongs in the 6mm to 9mm cavities found in triple glazed units. If a quotation offers krypton in a standard double glazed unit, ask what the cavity width is before agreeing to the upgrade.
Gas Is the Smallest of the Levers
It is worth keeping the contribution in proportion. Heat reaches an interior by radiation, conduction and convection, and different measures address different paths. Ranked by effect in a Gulf climate:
- Solar control coating. Reflects a large share of solar energy before it enters. In the UAE this is the single biggest lever, because the problem is keeping heat out.
- Low-E coating. A microscopically thin metallic layer that reflects long wave infrared. Which surface it sits on changes its behaviour.
- The cavity itself. Going from single to double glazing is a step change. Nothing else on this list compares.
- Argon fill. A worthwhile refinement on top of a cavity that is already the right width.
- Warm edge spacer. The perimeter spacer is a thermal bridge. An aluminium one conducts heat straight around the edge of everything the coating achieved.
- Thermally broken frame. Without it, the frame undoes the glass.
- External shading. Louvres, pergolas and deep reveals stop sun before it reaches the glass, and cost less per unit of heat than any coating.
Argon sits fourth. It is real, it is cheap, and it is not the thing that will decide whether a room is comfortable in August. A quotation that emphasises the gas fill while saying nothing about coatings or thermal breaks has its priorities in the wrong order.
Four Things to Be Careful About
You cannot see it, and neither can your installer
Argon is colourless and odourless. There is no visual check, no site test, and no way to tell a filled unit from an unfilled one by looking at it. Verification requires laboratory instrumentation, and it is not something that happens on a villa project. In practice, a gas fill claim is a claim about a factory process you are taking on trust.
Ask for the fabricator's specification sheet for the units being supplied, not just a line item on a quotation. A named fabricator and a documented fill rate is meaningful. The word "argon" typed into a quotation is not, on its own, evidence of anything.
This is not an accusation against the trade. It is simply the nature of an invisible product: the paperwork is the only thing a client can actually inspect.
It leaks, by design
Every sealed unit loses some fill over time through the perimeter seal. Industry practice treats a loss rate of up to about 1% per year as acceptable, and well made units measure below that. The arithmetic still deserves attention. At the accepted ceiling, a unit is materially less gas filled two decades in than it was on day one, and the performance drifts with it.
This is an argument for seal quality rather than against gas. The seal is what retains the fill, so a unit from a fabricator with good sealing practice will hold its specification far longer than a cheaper one that was filled to the same percentage on the day it was made.
The gas only works at the right cavity width
Covered above, and worth repeating because it is where specification errors cluster. Gas and cavity width are a matched pair. Choosing one without reference to the other produces a unit that costs more without performing better.
Seal failure takes the gas and the clarity together
When a perimeter seal fails, the fill escapes and moisture enters. The visible symptom is misting or a permanent haze between the panes that cannot be cleaned, because the affected surfaces are inside the sealed cavity. By the time a unit looks foggy, its thermal performance has already degraded. A fogged unit is replaced, not repaired.
What We Specify, and Why
For double glazed work in the UAE, Diamond Step® specifies argon in a cavity sized for it, behind a solar control Low-E coating, in a thermally broken frame, with a warm edge spacer where the project warrants it. The order of that sentence is deliberate: the coating and the frame decide the outcome, and the argon is a sensible refinement on top of a unit that is already correctly built.
We would rather talk a client out of a gas upgrade and into a better coating, or into external shading, than sell an invisible improvement that does less. On a west facing elevation, shading the glass usually beats upgrading it, and that conversation tends to be more useful than any argument about fill gases.
