Inside Bi-Fold Thermal Shutters 

This is from an article in the San Francisco Chronicle web site www.SFGate.com

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These are high R value inside shutters that could be very attractive and thermally efficient.

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Note the comments on preventing condensation on the inside of the windows.  Any tendency for condensation will depend on your climate, the current windows (single or double glazed), and the humidity levels inside the house, but its something to keep an eye on.