To enhance the thermal insulation performance of insulating glass, inert gas can be injected into its air cavity. This simple modification is a proven way to boost energy efficiency.

Gases used for this purpose must have a higher density than air. Why? A higher density slows down gas convection, which in turn reduces heat transfer through the glass.

Currently, argon is the most widely used gas for insulating glass filling— and for good reason.

Argon is a colorless, odorless, and non-toxic inert gas. At 0°C, it has a density of 1.7836 kg/m³—significantly higher than air’s density (1.2928 kg/m³) under the same conditions. It is also UV-resistant (so it won’t affect visible light transmission) and makes up 1% of the air we breathe, making it the most economical inert gas option.

Other inert gases can also be used for insulating glass, including xenon and krypton. However, these are much more expensive. At 0°C, their densities are 4.56 kg/m³ (xenon) and 2.86 kg/m³ (krypton), respectively. Like argon, they offer excellent stability and low reactivity.

The amount of gas needed depends on the internal volume of the insulating glass cavity. As a general rule, the gas required per unit of insulating glass is 1.5 times the volume of its cavity.

Since the filled gas is denser than air, the correct filling method is critical. Install the gas inlet at the bottom and the air outlet at the top—this setup ensures optimal filling quality (concentration) and shortens overall filling time.

Insulating Glass Inert Gas Filling

There are two primary methods for filling inert gas into insulating glass: manual filling and fully automatic online air curtain filling. Each has its own advantages and considerations.

Manual filling requires careful control of inlet and outlet speeds. If the inlet speed is slower than the outlet speed, filling takes too long and reduces production efficiency. Conversely, if the inlet speed is faster, gas turbulence forms in the air layer—also delaying the time needed to reach the required concentration. Worse, excessively high inlet speed can push internal pressure above normal atmospheric levels, causing the glass to break.

The fully automatic online air curtain filling method avoids these issues. During filling, the two glass panes are separated, and gas is injected from the bottom up. This design guarantees both fast filling speeds and consistent gas concentration.

When it comes to inspecting gas filling quality, China currently has no national standards. Internationally, there are two major inspection systems for insulating glass: the European Standard (EN 1279) and the American Standard (ASTM 2188/89/90). Notably, only EN 1279 includes specific requirements for testing inert gas filling quality.

Part 3 of EN 1279 outlines long-term testing methods and requirements for argon leakage rates and concentration tolerances. Its goal is to ensure the inert gas in the cavity remains sufficient to maintain the glass’s thermal or sound insulation performance throughout its service life. Part 6, meanwhile, focuses on production-stage quality control, specifying tolerances and requirements for the initial gas filling concentration.

Insulating Glass Inert Gas Filling

The required initial concentration is 85%, with a tolerance range of -5% to +10%. This means the acceptable concentration for new insulating glass falls between 80% and 95%.

Both Parts 3 and 6 of EN 1279 specify gas chromatography as the standard method for detecting inert gas concentration. This process involves extracting a gas sample from the insulating glass cavity and analyzing it with specialized equipment.

Here’s a simplified breakdown of the detection process: First, a sampling plug must be pre-installed during the insulating glass manufacturing process. During testing, an airtight syringe is inserted into this plug to extract gas from the cavity. The gas is then injected back into the cavity, and this “draw-and-inject” cycle is repeated twice. Finally, a clean gas sample is drawn into the syringe, injected into the adsorption column of a gas chromatograph, and the resulting chromatogram is recorded for analysis.

This method offers two key advantages: high accuracy and a wide detection range. It can measure any inert gas concentration between 5% and 100% reliably.

However, it also has significant drawbacks:

1. It is a destructive test—once performed, the insulating glass’s sealing performance is permanently damaged.

2. Testing takes a long time: Inspecting a set of 20 gas-filled panes requires at least 8 days, and up to 14 days in full compliance with EN 1279.

3. Equipment costs are high, and testing requires trained professionals.

4. It is limited to laboratory settings—impossible to use on-site at construction projects or for existing buildings.