Double-pane windows, also called "insulated" or "thermal" windows, are made with two panels of glass sandwiched over a spacer and sealant, creating a space between the panes that is filled with ...

Because air is a poor thermal conductor ... by touching the inside of a window on a cold day. If it’s single-pane glass, it will feel cold. If it’s double- or triple-pane, it won’t.