RFID Pocket Protection
Since RFID tags may be sensitive, and are easy to steal information from, some textile hackers built a faraday cage for their jean pockets. They replaced their cotton pockets with electromagnetic field shielding fabrics, which can be bought online for about $13USD per foot. The guys who did this simple hack even have a howto video to watch.
I imagine this fabric would restrict cellular frequencies too, and would be a good substitute for tin foil hats.