A thermal curtain is not your regular curtain that blocks a little bit of light and allows illumination in the room with no direct vision to the outside world. Thermal curtain are made up of multiple layers of fabric closely attached to one another with an aim to act as an insulator. Heat is trapped inside and the freezing air from outside doesn't affect that much. It is imperative to have your home drapes done with thermal curtains in case you are in the snow caps or near the chilly areas. It's not just an effective way to keep the heat inside, they also act as a good sound insulator as with multiple layers the decibel level is reduced for the outside world.