Alternative to signal jammers?

This is a neat solution to leaky wireless signals (as well as mobile phones in the cinema). Researchers at University of Morioka in Japan have invented magnetic wood, a material that blocks radio signals. Rather than using the rather crude approach of a signal jammer (which is illegal in the UK anyway) you line the walls of your building with this stuff and it stops various frequencies getting in or out. Stop the boss ringing you at the weekend while securing your WLAN. Nice.