How do curtain rods work?

Curtain rods are a device that allow heat to escape through a curtain when it is closed, rather than when it’s open.

When a curtain is closed with curtain rods, the hot air will escape through the back of the curtain.

When it is open, the curtain rods will hold the heat in.

Theoretically, this is the best way to maintain a curtain’s ability to keep cold air from escaping.

Curtain rod manufacturers are hoping to get this technology into the home, but they are fighting to win approval from regulators, who say curtain rods have a number of safety risks.

The Globe’s Chris Murnaghan reports.