Many modern routers don't allow the WiFi signal to be turned off so shielding is the only option. Also many routers now have VOIP phone systems which means they need to be switched on all the time.
 
If you need to block the WiFi signal, this is the ideal cover. The size of 9.8 inches x 15.7 inches means it is large enough for most domestic routers.
 
This faraday cover will suit both 2.4GHz and 5GHz frequencies.