Interesting...black painted cardboard for solar window heater. This simple device a traditional window & turnd it into a simple sun powered heater. Materials: Large piece of corrugated cardboard, Black paint, Paintbrush, Knife or scissors. South-facing window (east or west is okay but not as good). Blogger says zzz'air flowing in the bottom at 63 F and back out the top at a little over 100 F. Pretty hot for a piece of painted cardboard. The temperature outside is about 35 F."
Heat Reducing Window Film: Apply a simple transparent film to reduce heat gain from direct sunlight. Install special window films to reduce heat gain from sunlight or reduce heat loss in cold weather. It's a quick and easy task. -Keep rooms cooler with heat control window film -Buying and installing window film