Tin Foil Hat

When a writer wants to establish a character as a Conspiracy Theorist, a Crazy Survivalist, or another kind of paranoid weirdo, they usually give them hats made out of tinfoil to wear, ostensibly to protect themselves from The Government's Mind Control rays.

As The Other Wiki can tell you, however, aluminum actually has very little shielding effect and covering just the top of the head with it leaves the rest of the body (including the bottom of the head) "unprotected", anyway. So whoever is wearing it must be... funny in the head to begin with.

For when a Tinfoil Hat actually does protect the Properly Paranoid wearer, see also Artistic License Nuclear Physics. This trope includes both properly paranoid and simply paranoid examples.

Film -- Live-Action

 * Most of the main characters in Signs wind up wearing one at some point before the end of the movie.

Film -- Animated

 * The Futurama movie Into the Wild Green Yonder featured a cult-like group of hobos called the Legion of Madfellows who all wore such hats to prevent the Dark One from reading their thoughts, and indoctrinated Fry into their practices. They were, of course, Properly Paranoid.
 * The hat also serves to block Fry's own mind reading powers as he can't turn them off of his own accord.

Literature

 * In the early Artemis Fowl books, the paranoid centaur Foaly always wears a tin-foil hat.
 * The novel Idiots In The Machine by Edward Savio portrays a character who believes that tin foil keeps harmful gamma rays away and becomes a media sensation, marketing a successful line of foil hats to Chicago.
 * In The Dark Tower, Randall Flagg has one of these. Allegedly, it actually works against most forms of mind control magic, but it doesn't work on the villain he's facing, Mordred.
 * Inverted in The Salvation War, where demonic mind control and illusion powers can be blocked by foil and the story gets much mileage out of this, including the line "There will always be eccentrics who deny that the tin foil hat is absolutely essential to prevent baldricks taking over your mind."

Live Action TV

 * Eastenders character Joe Wicks was briefly portrayed constructing and wearing his own tin-foil hat as part of a storyline which saw him suffering from schizophrenia.
 * In an episode of Stroker & Hoop entitled Tinfoiled again (a.k.a. Star Crossed Livers), Stroker wore a tin foil hat to protect himself from being psychically manipulated by Ron Howard.
 * In The X Files, The Lone Gunmen wear them occasionally. Also, a policeman suggests they all get one in their Origins Episode when he realizes what kind of kooks he is dealing with.
 * On an episode of Fringe Walter wears a tinfoil hat at Massive Dynamic headquarters to defend against mindreading/MindControl projects, and convinces Astrid to do the same. In context, it's actually a credible concern.
 * NYPD Blue: While on desk duty Sipowicz gets a call from a psychotic Conspiracy Theorist. Sipowicz suggest (in as close to Sincerity Mode as possible) that he make a tin foil hat in order to block the rays the government is allegedly sending to his head.
 * In an episode of The Finder the Finder wears an aluminum foil hat. The client (Hodgins from Bones) mocks him, but it really does help block the government from interfering with your brain waves so you can move.

Music

 * In Doctor Steel's web video, "Reality Engineering", Steel is shown wearing a tinfoil hat when he's labeled a conspiracy nut.

Video Games

 * The tin-foil hat was an April Fool's Day item created by Blizzard to parody player paranoia about their character information being searchable on the World of Warcraft armory.
 * LA Noire features a street mission in which Phelps has to chase down a tinfoil hat-wearing conspiracy theorist.
 * Dogen Boole in Psychonauts wears a tinfoil hat he claims prevents him from accidentally making people's heads explode with his Psychic Powers.

Web Original

 * SJ Games used to (still does?) run a site cataloging weird things you might find in a Secret Government Warehouse. One of them was a crate of instruction booklets on how to make a tin-foil hat. They were all stamped "obsolete" and there was a note in the inventory saying that the mind-control system had been upgraded since printing, so tin-foil hats were no longer effective.
 * A guy wearing a tinfoil hat is the symbol of the Wild Mass Guessing section of This Very Wiki.

Western Animation

 * Exagurated in an episode of The Simpsons, "Brother's Little Helper", Bart becomes paranoid after taking an ADD drug called Focusin, leading him to believe that Major League Baseball is spying on him and begins donning a tin foil bodysuit. At the end of the episode, Bart turns out to be right when he shoots an MLB satellite out of the sky.
 * On Regular Show, Mordecai and Rigby make foil hats when using Pops' '80s era cell phones, after he warned them that they cause tumors.