The shutters are fine for giving you a layer between you and the glass, but they have lots of leaks on the sides, top, bottom and through the slats.
The old-fashioned ( Victorian 1860-1900)use of sheers, shutters, and heavy velvet lined drapes, all together, for winter made layers and folds that worked quite well.

Interior window shutters have the highest R value.

You may want to check out this link to view detailed information about shutter R value, compliments of SmartEnergy Living.

http://shutters4all.blogspot.com/

Here is a link that might be useful: All About Window Shutters

I think I've gotten the biggest bang for my buck with a combination of window treatments, not just one.

Last winter we added the bubble wrap to the windows - that gets an A+ rating at our house. Not only added R-value, but no more moisture dripping from the windows to wipe up each day (WOOHOO!!!). I'd suggest this no matter WHAT type of additional covering you might choose.

The next layer is Levolor blinds (honeycomb), on ALL windows, which fit inside the window casing very close to the windows. Good for insulating from the cold, but were much better with the bubble wrap layer on the window. The Levolor blinds also allow light to filter into the rooms even with bubble wrap on the windows.

Our bedroom windows also have room-darkening insulated curtains with a fabric pelmet over the top of the window. The curtain is installed under the pelmet and can easily slide open and closed on the rod. We're going to install wooden pelmets and more insulated curtains in other rooms before next winter since it worked so well. We even have a pelmet and insulated curtains over our front door. We get a lot of heat from the sun reflecting off the neighbors garage doors in the summer, so they help to keep the heat out in the summer, and the cold out in the winter.

BTW - We only have east and west windows and get little heat gain, so covering windows in unused bedrooms is a good thing... If you have south windows that you can take advantage of heat gain during the day, you may want to plan on coverings that are easy to open and close.

If you are freaked about not seeing out using bubble wrap on the windows, it's only for 2-3 months - it can be on windows you don't need to look out of. We keep one window only covered with a Levelor blind because its one we like to look out to the back yard. But it got so cold here last winter we ended up adding bubble wrap for severl of the coldest weeks and looking out be damned.... The additional R-value was well worth it. Besides, it takes one jerk to remove the bubble wrap, and a quick spritz of water to install it again. NO big deal...

In another house I went to a lot of trouble and made insulated window quilts for all our windows, but once again, they are layers of materials, not just old quilts placed over a window. I found the instructions on-line. They can also be ordered from different companies.

- a layer that is water-proof (because windows accumulate moisture in the winter and the damp will ruin or stain cloth) - I used mylar emergency blankets (they cost 98 cents at Wal-Mart in the camping department).

- a layer or two of insulating quilt batting

- a decorative fabric layer - I used thin quilted bed spreads I found on sale that were perfect for the project, and that layer served as an additional layer of quilted insulation.

- quilted it all together

- They also fit tightly into the window on all sides so that you don't get the chimney effect from air-flow. You can use hook and loop fastening around 3 sides to secure the window quilt as close as possible to the window. I used strips of plastic magnets (metal magnets will rust, so I don't suggest them).

You can make them so they roll up like a roman shade, or you can use the "tent door" method where you pull one bottom corner up and attach it via a hook and loop, a loop and button, or loop and frog, to open an angled flap similar to a tent opening.

You lose a lot of your efficiency if warm air can travel from the bottom of the covering, cooling as it passes the cold glass, up through to the top of the window over the rod or any opening. Cold air enters the room again - no matter how energy efficient the material covering the window might might be. Closing that air gap is crucial! So just a covering of insulated curtains on the outside of the window isn't the best answer because of the chimney effect. To prevent the chimney effect, you can install a cloth or wooden pelmet over the top of the window where the curtain rod will hang, or fit the covering inside the window casing, not outside the window.

We're going to build wooden pelmets because they can be left as an architectural covering on the window if you want to remove the curtains. The curtain rod can be installed in the wooden pelmet, not on the window. You can even use a simple tension rod under a wooden pelmet.

-Grainlady