WiFi blocking paint additive

Need to totally lock down your Rec Room WiFi network? Then you definately need this paint additive - it makes the paint into a Faraday cage to block radio waves in the WiFi band. This will also block incoming radio interferance (aka your neighbors WiFi network). Since it reflects the WiFi signal, it should (theoretically) improve the signal strength inside the room to. Assuming, of course, it really works. They should do something similar for cell phone signals to allow restaurants and movie theatres to passively block signals so people can't get cell phone reception (actively blocking cell phones is illegal in the US).