Advice 1: Glazing unit

Spaces between the glass panes are called chambers, the more chambers (glass panes), the wider and warmer the glazing unit and lower the Uw of the window.

A glazing unit is in fact a ready module of two or three glass panes sealed with a special sealant. They are divided with a spacing bar, and the space between is filled with a special gas, usually argon. Replacing the air with a gas that has lower heat transfer coefficient lowers that coefficient for the entire glazing unit.