Here is a nice handwaving on the subject. Conclusion: R = 2, which at least isn't nothing.
www.rebresearch.com/blog/the-joy-of-curtains/
Also, the R value of bubble wrap is most likely 1
www.greenbuildingadvisor.com/community/forum/general-questions/19778/bubble-wrap-window-insulation-testing
www.builditsolar.com/Projects/Conservation/bubblewrap.htm
