We have metallic radiant shielding on our roof decking. We have not noticed any Wi-Fi signal variance since replacing our roof, which included the addition of the radiant shielding.

Click on the following maps.google.com link and then click the zoom one extra time for maximum zoom to view from around 2,200 feet above:
http://maps.google.com/maps?ll=-23.547585,-46.6650 51&spn=0.005375,0.007918&t=k&hl=en
...then compare it to Google Earth zoomed to around 500 feet above:
http://www.radojevic.com/-23.547585,-46.665051%20( 500%20ft%20above).jpg
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