One simple way to insulate single pane windows for the harsh winter months is to look no further than bubble wrap. The insulating properties of bubble wrap can actually double the efficiency of windows, and it couldn't be any easier to do. Just fill a spray bottle with water and cover the entire window with a fine mist. Cut bubble wrap to size and place on top of the glass. That's it. It'll stick for as long as you want, and you can easily remove it when you no longer need it.