[[quoteright:162:[[WesternAnimation/LittlestPetShop2012 http://static.tvtropes.org/pmwiki/pub/images/russell-tinfoilhat_2454.jpg]]]]
[[caption-width-right:162:Russell conducting some WildMassGuessing.]]

->''"I seem to recall it was your bright idea to spend billions of credits on those orbiting [[HypnoRay mind-control lasers]]!"''
->''"How was I to know that tinfoil hats would become the latest fashion?"''
-->-- '''Plan 7 of 9 from Outer Space''' by Odon

When a writer wants to establish a character as a ConspiracyTheorist, a CrazySurvivalist, or another kind of paranoid weirdo, they usually give them hats made out of tinfoil to wear, ostensibly to protect themselves from TheGovernment's MindControl rays.

As TheOtherWiki can tell you, however, aluminium 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. (In fact, if improperly made, the tinfoil could amplify any radiation reaching the head.) So whoever is wearing it must be... funny in the head to begin with. Or the more sinister interpretation: [[spoiler: the whole idea that tinfoil will protect you is Just What They Want You To Think.]]

To elaborate : To shield off radiation, you need steel. Electromagnetic waves consist of alternating areas of electric fields and magnetic fields. To reflect them, you need a material, that shorts both electric fields and magnetic fields. In terms of shorting electric fields, any metal (being conductors) does an adequate job (aluminium (which so called tinfoil is usually made of, despite its name) is even a very good conductor), but to short magnetic field you need a ferromagnetic metal, like iron, nickel or cobalt. As iron is seldom used nowadays, the best choice is steel (an alloy of iron,carbon and tiny amounts of other components). Just take a look at a video-recorder: Videorecorders may have fancy chassis made of aluminium, but if you look inside, you will see a small box behind the coaxial connectors, there the aerial is connected, containing the high frequency circuitry. This box is made of steel in order to shield the radiation.

For when a Tinfoil Hat actually ''does'' protect the ProperlyParanoid wearer, see also ArtisticLicenseNuclearPhysics and FantasticRadiationShielding. This trope includes both properly paranoid and simply paranoid examples.
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!!Examples:

[[foldercontrol]]

[[folder:Film -- Live-Action]]
* Most of the main characters in ''Film/{{Signs}}'' wind up wearing one at some point before the end of the movie.
** The scene from ''Signs'' gets parodied in ''ScaryMovie 3''
* More of a hat in spirit, in ''Film/Series7TheContenders'', the ceiling of competitor Franklin's trailer is lined with tinfoil, and his personality follows suit (YMMV on whether it's played straight--along with the rest of the movie).
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[[folder: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.[[note]]Fry's hat in particular would be in different shapes for different scenes (it's foil, after all), depending on the occasion. E.g. it became a stereotypical police officer hat when he was posing as a security guard.[[/note]] They were, of course, ProperlyParanoid.
** The hat also serves to block Fry's own mind reading powers as [[PowerIncontinence he can't turn them off of his own accord]].
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[[folder:Literature]]
* In the early ''Literature/ArtemisFowl'' books, the paranoid centaur Foaly always wears a tin-foil hat. In the second book he throws it away in frustration after being trapped in his own hermetically sealed command center.
* 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 ''Franchise/TheDarkTower'', 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 ''TheSalvationWar'', 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."
* In ''Literature/TheAlloyOfLaw'', because of [[MagicAIsMagicA the way the magic system works]], aluminum blocks [[EmotionControl emotional allomancy]], so wearing a tinfoil hat can in fact protect you from mind control.
* In the ''[[Literature/TowerAndTheHive Pegasus]]'' trilogy, one character wears a metal skullcap to block out mind-reading. This is actually effective against telepaths in this 'verse. [[spoiler: Doesn't help much if the psychic has made skin-to-skin contact, though.]]
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[[folder: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 ''TheXFiles'', TheLoneGunmen wear them occasionally. Also, a policeman suggests they all get one in their OriginsEpisode when he realizes what kind of kooks he is dealing with.
* On an episode of ''Series/{{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.
* ''NYPDBlue'': While on desk duty Sipowicz gets a call from a psychotic ConspiracyTheorist. Sipowicz suggest (in as close to SincerityMode 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 ''Series/TheFinder'' 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.
* In the fourth season of ''Series/{{Farscape}}'' a Sheriff (or deputy) encountered by Moya's crew when they land on Earth in 1985 via time travel turns up again showing off a tinfoil-lined baseball cap on TV in 2003 when the crew returns. In his defense, he did receive several doses of one of Noranti's potions during the first visit.
* Oliver does this in ''Series/HannahMontana'', but it's really more of a parody, because he wants Joanie to think he's insane and dump him.
* ''{{Dollhouse}}''. Senator Perrin goes public accusing the Rossum Corporation of unethical practices, hoping that it will encourage witnesses to come forward. The following episode he's griping that the only witness so far is a guy in a tinfoil hat claiming that Rossum mailed his liver to Saturn.
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[[folder:Machinima]]
* Deconstructed in ''Machinima/FreemansMind'', where Freeman reasons that, assuming mind reading is possible despite not showing up on any known spectrum, a tinfoil hat would conduct any signal that the wearer is concerned about. He concludes that you'd have better chances with a lead helmet coated in rubber.
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[[folder:Music]]
* In DoctorSteel's web video, "Reality Engineering", Steel is shown wearing a tinfoil hat when he's labeled a conspiracy nut.
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[[folder:Tabletop Games]]
* ''TabletopGame/{{GURPS}} Illuminati'' actually gives a bonus on resisting Mind Control Lasers to people wearing a tinfoil hat.[[labelnote:fnord]]It's just +1 though, so it doesn't make much difference.[[/labelnote]]
[[/folder]]

[[folder: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 ''WorldOfWarcraft'' armory.
* ''LANoire'' features a street mission in which Phelps has to chase down a tinfoil hat-wearing conspiracy theorist.
* Dogen Boole in ''VideoGame/{{Psychonauts}}'' wears a tinfoil hat he claims prevents him from accidentally [[YourHeadASplode making people's heads explode]] with his PsychicPowers.
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[[folder:WebComics]]
* In ''{{Sinfest}}'', [[http://www.sinfest.net/archive_page.php?comicID=3498 Squigley's protection from the Illuminati.]]
* In ''Webcomic/{{Freefall}}'', [[http://freefall.purrsia.com/ff1900/fc01863.htm Edge's protection from the lobotomizing program.]]
* In ''TheGreeningWars'' Hatchet's old "friend" Codex was wearing a tinfoil hat when they visited his bunker. But then again his former employers had [[http://www.drunkduck.com/The_Greening_Wars/5345899/ put a tracking chip in his head]].
* Karl from ''Webcomic/FreakAngels'' wears one at all times to block his telepathic link to the rest of the group, because they mostly seem to use it for inane bickering, {{Seinfeldian Conversation}}s and complaining about how crap their sex lives are. AMindIsATerribleThingToRead indeed...
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[[folder:Web Original]]
* SJ Games used to (still does?) run a site cataloging weird things you might find in a SecretGovernmentWarehouse. 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. (Elsewhere in SJ Games's paranoia-inducting line of games is the note that ''aluminum'' foil beanies do not work against mind-control devices, but ''tin'' foil beanies did. This fact is behind the switch from tin to aluminum foil in the mid-20th century.)
* A guy wearing a tinfoil hat is the symbol of the WildMassGuessing section of ThisVeryWiki.
* The [[http://zapatopi.net/afdb/ Aluminum Foil Deflector Beanie]]
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[[folder:Western Animation]]
* {{Exaggerated|Trope}} in an episode of ''TheSimpsons'', "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 ''RegularShow'', Mordecai and Rigby make foil hats when using Pops' '80s era cell phones, after he warned them that they cause tumors.
[[/folder]]
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