If you live in a city, I would use curtains that shield against RFI, something with a metal braid woven inside them.
Good Materials for Curtains
Has anyone made heavy curtains specifically to add absorbance to a room, and (of course) to block the reflections of glass? If so, what materials did you use. This is such a simple and common acoustical technique, yet I can find little written about what types of fabric (etc) are best. Thanks for your experienced suggestions.