are there any window filters that block wifi?

I'm able to use a wifi network only when my window is open. Since I'm living in a student's building where you need to pay for inteet, it makes sense for the manager to try to block the wifi coection from the university which is on the other side of the street. It would also explain why they installed a metal grid outside half of the window... so not only for safety purposes. Still when I open the window I get coection, which is crazy. It wouldn't be crazy if wifi blocking window filters exist...