When shopping for new windows, you are likely to see ads like “Argon windows 30% off”, “Krypton windows 20% off” or “Low-E windows 40% off.” But while these terms sound technical and fancy very few homeowners actually know what they mean. Even fewer, whether these features are worth it or even necessary in their window replacement. In reality,  there are several unique technologies that combine together to make vinyl windows energy-efficient.

The Energy-Star rating, which is given to the best-performing windows usually means it combines most if not all of the following features:

The insulated glass unit in modern windows is filled with an inert gas to improve thermal performance.
The insulated glass unit in modern windows is filled with an inert gas to improve thermal performance.

We wanted to take some time to discuss gas fills as they tend to be one of the most popular options our customers ask about

In older units, the space between panes was filled with ordinary air. Most manufacturers today offer windows which have this space filled with an inert gas to further reduce heat loss and condensation. The term inert refers to chemically stable, non-reactive gasses that are safe for your home. Manufacturers usually use either Argon or Krypton, the first being a more common cheaper choice. Gas fills are considered a convenient option because they are invisible and odorless. Yet, a gas fill can increase the insulating value of a double-pane window to that of a standard triple-pane unit.

Argon gas fills

Argon is a natural choice for a gas fill because of its two unique qualities. It reduces conduction heat loss because it has a lower conductivity than air, as well as reducing convection losses because it is heavier than air and suppresses air movement between glazings. Because it is a more affordable option, most manufacturers will offer it as a standard option.

Krypton gas

Krypton gives a slightly better performance than Argon and permits for a smaller spacing between the panes. A narrow pane requires less of this expensive gas, and in turn allows for the construction of multiple glazed units with less chance of stress breakage. For maximum efficiency, Krypton is usually used in triple or quad pane units, and Argon in double-glazed or triple-glazed units.

Another added feature of gas fills in windows is their ability to significantly reduce outside sound, adding to the privacy of your home.

We often get questions from customers about the technology utilized in inserting the gas fills. Some companies like to talk about their unique process of filling panes with gas, but ultimately the process doesn’t differ from one manufacturer to another. What matters more is that the unit is sealed properly and the gas remains in the unit without being able to escape.


If you already have a consultation appointment or are considering booking one, make sure to ask about all the features that come standard in your modern window. These differ between manufacturers. Some companies include Low-E coatings in their units with gas fills as an upgrade while others offer gas fills upfront and coatings as an upgrade.

Check out these window replacement articles:
Find out what else makes an energy efficient window
Learn how much replacement windows should cost
See our full line of replacement window styles

Get a Free Quote For Energy Efficient Windows