blocking rf signals

tin foil

Are you sure? I'm looking to do some shoplifting for Christmas gifts pretty soon.

That's what that NSA dude from the movie Enemy of the State told Will Smith's character.

You're right, it seems to work on all radio frequencies according to the FCC.

Awright! I'm going shopping!

awesome flick...

What you seek is called a "Faraday Cage". Basically, they imbed wire mesh screen into the walls of the building while it is being built. Then you add filters to the power and signal lines that penetrate the wire mesh enclosure.

The U.S. Military's EMSEC program has very detailed guidelines for building desgins that render them electronicly silent.

Sheet metal could work. Here are some articles to learn more about this:

http://en.wikipedia.org/wiki/Faraday_cage

http://en.wikipedia.org/wiki/Electromagnetic_shielding

Use a material that is called mu (Greek) metal. And of course, it could be that building a Faraday cage could do it too. Super expensive to do, however. Be aware that sheet metal would have to using the right sort of metal.

Any conducting metal will do, and, as fishin said, it can be just a mesh. The criterion is that the mesh size is small compared to the wavelength.