http://www.atnuke.com/nuclear/lead/leadfoil.html
(http://www.atnuke.com/images/l/leadfoil.JPG)
Sorry, not for the pencil neck geeks among us. Hat weighs when made about 8-10 pounds. Shit you learn working for the DOD for 28 years.
Instructions
http://www.instructables.com/id/Aluminum-Foil-Hat/
Have it on good authority that Z rays can penetrate Aluminum foil. The Illuminati they ain't no dummies. Be prepared to fight your lizard overlords.
But I like lizards, particularly the dinosaur kind. Mammals are somewhat questionable though ;-)