I remove the screens from my windows and wrap plastic sheeting around them and then re-install the screens. This creates a translucent "second window" with an insulating air gap between the glass pane and the screen. It also seals the window better since the plastic around the screen's frame makes it a tight fit and very little air flows around it. I know it is effective because the condensation I used to have on the windows, and resulting mold, has completely ceased to occur. My electric bill went down noticeably. I also installed good quality storm doors on my front and rear entrances.
I remove the screens from my windows and wrap plastic sheeting around them and then re-install the screens. This creates a translucent "second window" with an insulating air gap between the glass pane and the screen. It also seals the window better since the plastic around the screen's frame makes it a tight fit and very little air flows around it. I know it is effective because the condensation I used to have on the windows, and resulting mold, has completely ceased to occur. My electric bill went down noticeably. I also installed good quality storm doors on my front and rear entrances.