A type of wallpaper that prevents Wi-Fi signals escaping from a building without blocking mobile phone signals has been developed by a British defence contractor. The technology is designed to stop outsiders gaining access to a secure network by using Wi-Fi networks casually set up by workers at the office.

via Stealth wallpaper keeps company secrets safe – 08 August 2004 – New Scientist.

Copper coated

Solid metal antennas normally give a very strong reflection to enemy radar scanners. To hide them, FSS sheeting can be electrically set to allow through only the precise frequency the antenna wants to transmit and receive, while absorbing all other frequencies including those of the incoming radar.

BAE’s anti-Wi-Fi wallpaper is made from a 0.1-millimetre-thick sheet of kapton, the same plastic used to make flexible printed circuit boards in lightweight portable gadgets like camcorders. The kapton is coated on each side with a thin film of copper.