From a professional colleague...
Q. "I would like to know if there is any security film that can be applied to windows to help block RF emissions. I have heard of curtains that are made for purpose? not sure though? Any ideas would be appreciated. Thanks."
A. Their are all sorts of RF shielding materials on the market: window film, speciality glass, screening, wallpaper, paint, gaskets, curtains, beanies, etc. Each item, by itself, is not a very effective solution. Used in conjunction with one another, RF may be attenuated to a point where it solves a particular problem. The attenuation will not be 100% unless one constructs a fully shielded room (Faraday cage). In government circles these specially built rooms are called Sensitive Compartmentalized Information Facility, otherwise known as a SCIF. Even then, the slightest crack or deformed door gasket will allow RF in/out.
100% shielding becomes problematic when the application is eavesdropping countermeasures. Shielded rooms are ugly and expensive, and other methods are not 100% effective. In counterespionage and TSCM, the information is either protected, or it is not protected.
