Yes, you've read it right. Such thing exists.
This passive baby contains particles of aluminum-iron oxide, which resonates at the same frequency as wifi and other radio waves. Costing at £10 per kilogram, the said paint can block frequencies all the way up to 100GHz, although a 200GHz-blocking pigment is on its way. This was developed by the University of Tokyo.
Since the paint can block a wide range of frequencies, it could also end the problem of noisy cellphones inside the cinema. All you have to do, is paint the walls of the cinema and viola, instant cellphone jammer. A sample is on the way to one American Company, which would try this creation in their very own cinema. Says this could also open a new way to a higher screen resolution.
Though the new material promises a number of technological advantages, some security experts remain unconvinced by a bucket of this paint. Painting the building for the sake of Wi-Fi security is more expensive than complex than the security functionality readily available in even the cheapest of Wi-Fi access points.
For the full article, refer to this. photocredits: http://www.2dayblog.com/images/2007/march/wifi_paint.jpg