Argon gas is used to increase the energy efficiency and general performance of thermal windows. Thermal windows, also called insulated glass units, or IGU, are either double-pane or triple-pane, meaning each section of window has two or three layers of glass with a sealed space in between. The spaces are filled with argon or other gasses to slow the transfer of heat through the window. Gases like argon are preferable to air because air contains moisture that can condense on the inside of the glass units, making the window cloudy. Air also insulates less effectively than gas fills. Argon is an inexpensive, non-toxic, colorless, and odorless gas that occurs naturally and constitutes less than 1 percent of Earth's atmosphere.

Benefits of Argon Gas in Windows

Almost all thermal windows today use some type of gas fill, so the benefits of argon are similar for most new thermal windows.

Improves U-value, the measure of a window's thermal performance; similar to the R-value of wall insulation

Enhances soundproofing characteristics

Minimizes heat exchange through the window

Reduces the possibility of condensation and frost

Can be used in all climates

Can be combined with low-E coatings for optimal window performance

Available in residential and commercial window sizes and styles

Does not corrode window material as oxygen will

Does not contaminate the environment; non-toxic gas

Does not add significantly to window cost—adds $30 to $40 per window—but helps achieve significant long-term energy cost savings

Drawbacks of Argon Gas in Windows

The only real drawback of argon gas vs. other types of gas fill is that argon is not the most energy efficient gas available. In general, thermal windows present some drawbacks and important considerations.

Argon gas fill does not expand or contract; however, glass does, and it this can eventually destroy the seals that contain the gas between the glass panes.

Gas fills leak from window even when the seals are intact. The leakage rate is expected to be 1 percent per year, at best.

If the window seal has even a small gap in it, the argon gas will escape and will be replaced by moisture-laded air. When the window loses a significant portion of gas, it will be noticed. Condensation will build up inside the window, indicating that the seal is broken.

Metal spacers may not perform as well as non-metallic spacers, for leakage, heat transfer, and soundproofing.

Argon vs. Krypton Gas Fill

Most thermal windows are filled with argon or krypton gas, but some use a combination of these gasses and/or xenon, nitrogen, or oxygen. The main differences between argon and krypton windows are cost and energy efficiency. Windows with krypton fill tend to have lower U-values (better insulating quality) and are more expensive than argon-filled windows. Argon typically represents a better value overall, especially with double-pane windows. Being cheaper, argon is usually used to fill the wider 1/2-inch spaces between panes in double-pane windows, while krypton, with its better insulating quality, is often used for the thinner 1/4- or 3/8-inch spaces between panes on triple-pane windows.

Like argon gas, krypton is odorless, colorless, and non-toxic. Neither gas poses any risk to building occupants due to gas leakage. The decision between argon and krypton usually comes down to the lifetime cost of the window, factoring in the purchase price and the energy cost savings of the window over its lifetime.