Glazing fill gas: air, argon, or krypton?

Understanding the role of gas in an insulating glass unit

What happens between the two panes: conduction, convection, and radiation

In a double-glazed unit, the space between the panes isn't "empty." That's where the heat loss happens. Conduction carries heat through the gas. Convection creates small air movements that also carry heat. And radiation is the "at-a-distance" exchange between warm and cold surfaces.

Air, argon, krypton: differences in density and heat transfer

Air works, but argon is denser and better restrains convection. The result: the glazing gains in performance without driving up the cost too much. Krypton goes further. It restricts heat transfer even more, especially when the gas gap is thinner. That's useful on window frames where the available depth is limited.

When gas isn't enough: the importance of spacer bars and low-emissivity coatings

Gas doesn't do everything. A "warm edge" spacer bar reduces the thermal bridge at the edge of the glazing and helps limit condensation. And a low-emissivity coating reflects part of the thermal radiation back inside. This duo is often what makes the difference on the Ug value.

Argon: the most common choice for improving glazing performance

Typical gains on the Ug coefficient: what to expect on site

On double glazing with a low-emissivity coating, replacing air with argon often gains around 0.2 W/m².K on the Ug value. In practice, you frequently go from a Ug close to 1.3 down to 1.1, depending on the makeup. It's not magic, but it's a net gain, without changing the look of the glazing.

Gas gap thicknesses and compatibility with standard double glazing

Argon works very well within "standard" spacer thicknesses. A gap around 16 mm remains the most common in a 4/16/4 configuration, and it's compatible with most window frames designed for double glazing. If the gap is too thin, the gain drops. If it's too thick, convection returns and part of the benefit is lost.

Points of vigilance: fill rate, seal integrity, and durability

The result mainly depends on the manufacturing process. Aim for a high fill rate, with end-of-line checks, and good perimeter sealing. A poorly fitted seal or a low-end spacer bar can let the gas escape over time. On site, check compliance (marking, product data sheet) and favor manufacturers that guarantee long-term performance.

Krypton: mainly useful for very high-performance glazing and tight spaces

When krypton offers a real advantage (triple glazing, thin gas gaps)

Krypton is worth considering when you're aiming for very well-insulated glazing, with gas gaps thinner than usual. On triple glazing or on window frames with limited available depth, it restricts heat loss better than argon. The result: a few extra points on the Ug value without thickening the unit, which helps stay compatible with certain profiles and renovation constraints.

Extra cost and availability: how to decide without getting it wrong

Krypton is rarer, so more expensive and sometimes less available depending on the manufacturer and lead times. Decide using a simple criterion. If the goal is a very low Ug value in a tight space, it's worth the extra cost. Otherwise, a good, well-sized argon-filled unit often does the job. Require a clear product data sheet (Ug, spacer bar, composition) before pricing it.

Installation best practices to preserve the stated performance

A gas fill doesn't forgive mediocre sealing. Install on appropriate shims, respect the clearances, avoid stressing the perimeter seal, and check the continuity of the interior and exterior seals. A warm-edge spacer bar and careful installation also limit condensation at the edges.

Choosing the right glazing in 2026 based on use, zone, and the client's budget

Exposure, noise, summer comfort: adapting the glazing to the actual need

Depending on orientation and climate, the same glazing won't give the same result. To the south and west, aim for a good balance between solar gains and protection. Solar-control glazing helps with overheating, without turning the room into a cave. In noisy areas, favor acoustic glazing, often laminated, and also pay attention to the frame's airtightness.

Renovating a single-family home vs. a shared building: constraints and trade-offs

In a house, you're free to weigh double vs. triple glazing based on budget and overall insulation. In a shared building, the issue is often facade uniformity. Colors, glazing bars, opening styles, and ventilation can be mandated. Anticipate the time needed for a vote in the general assembly and check local rules if the building is protected.

Grants and requirements in 2026: points to check (RGE, technical data sheets, supporting documents)

For grants, the company must be RGE-certified and the performance must be justified. Request the technical data sheet with the Uw and Sw values, and keep the quote, detailed invoice, and end-of-works certificate. On the CEE side, check the operation sheet applicable to windows before starting the job.

How to check glazing performance and reassure the client

Reading a product data sheet: Ug, Uw, solar factor, and light transmission

To assess glazing, start with the product data sheet. Ug measures the heat loss of the glazing alone — the lower it is, the better. Uw covers the complete window, glazing plus frame, and is the most meaningful figure for the client. The solar factor (g) indicates how much sunlight gets in, useful for weighing summer comfort against free solar gains. Light transmission indicates clarity, especially when renovating window openings.

Spotting markings and labels: CEKAL, CE marking, traceability

On the spacer or at the edge of the glazing, look for a legible marking. The CEKAL label is a recognized reference for insulating glazing units. The CE marking on the window frame refers to a declaration of performance. Ask for the reference, batch, and date. With this traceability, you can show the client where the product comes from and what it's worth.

Common mistakes to avoid: thermal bridges, weatherproofing, frame adjustments

Good glazing can disappoint if the installation is poor. Watch out for: thermal bridges around the perimeter, weatherproofing that's too thin or discontinuous, and poorly adjusted opening sashes that let air through. After installation, check seal compression, closure, and run a simple smoke-pencil or hand test near the corners.