http://www.pcgamer.com/you-can-actually-improve-your-wi-fi-signal-with-aluminum-foil/

If you're old enough to remember rabbit ears on televisions, then you probably at some point played around with wrapping aluminum foil on the antenna to improve the signal. Fast forward a few decades later and you might still want to use aluminum foil to improve signal strength, only now for your wireless router instead of your TV.

Xia Zhou, an assistant professor of computer science at Dartmouth College, is getting ready to present research at ACM's BuildSys 2017 in Delft, Netherlands, that outlines how a customized reflector placed on a router's antennas can direct wireless signals where they are most needed.