Argon gas fill

Argon is a colorless, harmless gas that is heavier than air. Makers pump it into the sealed space of an IGU before the unit is closed. It slows the circulation of air inside the gap, so less heat crosses from the warm pane to the cool one.

The gain is real but modest on its own. It works best with a low-E coating and a warm edge spacer. Some gas leaks out over decades, so ask about the seal and the glass warranty. To see how it lowers your U-factor, read how to read an NFRC label.