I also have single pane windows that are drafty in the winter, and curtains just aren’t enough, as the draft moves around it.

You can use the plastic as a second bubble of insulation by trapping an air layer between it and the window. You simply tape the plastic to the window frame, all the way around, and the trapped air bubble with help equalize any draft that comes through.

You can get kits for this that can be more easily removed if you actually want to open the window, but I had assumed that if you’re trying to keep the heat in, you’re going to be sealing the window until spring.

Here’s a video showing the method I’m describing: www.youtube.com/watch?v=qQ2zinfyxQU