When a writer wants to establish a character as a Conspiracy Theorist, a Crazy Survivalist, or another kind of paranoid Cloudcuckoolander, 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, 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: 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, where the aerial is connected, containing the high frequency circuitry. This box is made of steel in order to shield the radiation.
Of course, this assumes the threat is actually radiative in nature.
For when a Tinfoil Hat actually does protect the Properly Paranoid wearer, see also Artistic License Nuclear Physics and Fantastic Radiation Shielding. This trope includes both properly paranoid and simply paranoid examples. Compare also Manifesto-Making Malcontent, where manifestos are used as a similar material shorthand for potentially dangerous weirdos.
- Wander over Foster's AU One-Shot: Bloo being a conspiracy theorist is accentuated by his plans to make tin foil hats to protect his mind from being controlled by Wander. However, in this case, Bloo's theory that Wander is an alien is actually correct.
- 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 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.
- A variation on this trope is used in the film Conspiracy Theories. In it the main character lines walls of his house with tin foil to block out government surveillance tools. However this, (like many conspiracies in the film) are subverted and proven right. It's revealed that government tools struggle to penetrate his aluminum defenses.
- Joan Cusack plays a character plays a friendly snowplow driver credited as the "Tin Foil Woman" in the Netflix film Let It Snow. Bonus points for also lining her clothing with it. She point-blank refuses to explain why.
- The crazy conspiracy theorist in Noroi: The Curse takes it one step further and wears an outfit made of tin foil.
- More of a hat in spirit, in Series 7: The Contenders, 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).
- Most of the main characters in Signs wind up wearing one at some point before the end of the movie. The scene gets parodied in Scary Movie 3, where the hats are giant Hershey's Kisses.
- In the early Artemis Fowl 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.
- When James of The Chronicles of Steve Stollberg suggests that Mickey Mouse faked his death, Miss Jackson implies that he likes to wear tinfoil hats.
- 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.
- In Ever World, Senna gets into a mentally-ill homeless man's head, telling him he should have remembered to wear his tinfoil hat as she makes him go yell disturbing things outside Jalil's house.
- In I Sit Behind The Eyes, Terry's Uncle is an eccentric Parapsychologist who wears one for work. It doesn't do much good, as the title Entity enters people through the mouth.
- In the Mistborn books, aluminum cannot be affected by Allomantic powers, so adding it to a hat in The Alloy of Law protects the wearer against Emotion Control.
- In the Pegasus trilogy, one character wears a metal skullcap to block out mind-reading. This is actually effective against telepaths in this 'verse. Doesn't help much if the psychic has made skin-to-skin contact, though.
- 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."
- Played seriously in The War Against the Chtorr. The Telepathy Corps has been known to implant people without their knowledge, and even if you find out about it the only thing you can do is wear an iron cap for the rest of your life if you don't want thousands of telepaths being able to see and hear and feel everything that you're doing.
- Chuck in Better Call Saul wears a foil thermal blanket whenever he wants to go outside. Though not a true tinfoil hat (thermal blankets are made of plastic), when coupled with his belief that it protects him from harmful electromagnetic radiation, it definitely invokes the imagery.
- A variation in CSI: NY's "Consequences." A schizophrenic woman "captures" a badly injured paintball player, thinking he's an alien and that the green paint oozing all over his gear is his blood. She has metal colanders hanging from the ceiling throughout her apartment, and offers for Stella and Flack to put them on so their thoughts won't be captured. Naturally, they decline.
- 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.
- 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 the fourth season of 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.
- 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.
- On an episode of Fringe Walter wears a tinfoil hat at Massive Dynamic headquarters to defend against mindreading/Mind Control projects, and convinces Astrid to do the same. In context, it's actually a credible concern.
- The Glades: The Victim of the Week of the "Close Encounters" episode was a millionaire who believed that he was abducted by an UFO and had a few foil hats scattered through his mansion.
- On Good Eats, Alton wears a foil fedora and a metallic suit, while he's inside of a grill, explaining how a grill works, how it can be a problematic method for cooking chicken, and how to get around these problems. Unlike most examples, it's not worn to keep radio signals from messing with his head or anything along those lines, but simply because it's cool.
- In an earlier episode about pot roast, Alton wants to use some foil for braising the meat while cooking pot roast at his neighbor Chuck's trailer home. There's no foil to be had in the kitchen, but there's plenty of it on the roof of the trailer, formed into a satellite dish. When questioned, Chuck responds that he got the idea from a neighbor of his who wears foil on his head to block mind-controlling signals from the government. Alton tells him to take the satellite dish down so they can use the foil for the pot roast.
- Oliver does this in Hannah Montana, but it's really more of a parody, because he wants Joanie to think he's insane and dump him.
- 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.
- Starsky & Hutch: Commander Jim from "Lady Blue" believes brain rays from Alpha Centauri are torturing and mind controlling him. To protect himself, he not only wears aluminum foil under all his clothes but also decorates his entire apartment with it, even wrapping it around his desk lamps.
- 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.
- In Doctor Steel's web video, "Reality Engineering", Steel is shown wearing a tinfoil hat when he's labeled a conspiracy nut.
- "Weird Al" Yankovic's "Foil" (which is a parody of "Royals" by Lorde) has Al claim to have cracked the code on conspiracy staples such as The Illuminati, Black Helicopters, the Moon-Landing Hoax, and more, which is why he crafted a handy hat from foil, to protect himself from alien Anal Probing and mind reading. It doesn't do him much good, because The Men in Black just tranquilize him and drag him away. The music video ends with the director (played by Patton Oswalt) unmasking himself as a lizard person.
- GURPS Illuminati actually gives a bonus on resisting Mind Control Lasers to people wearing a tinfoil hat.fnord
- The Occult Adventures companion book for Pathfinder introduces the "tin cap" item, which grants its wearer a bonus to resisting mind-altering effects and divination spells that gather information about them, but saps the mind of the wearer and induces paranoia that makes the player throw a saving roll against any effect, including harmless ones. The book also introduces a more powerful "stannum crown", which provides complete immunity to the aforementioned effects, but can only be removed by the wearer and requiring a saving throw that grows more difficult the longer the crown is worn.
- In The Darkside Detective, one of Dooley's conspiracy theorist colleagues believes that wearing a tinfoil hat will help keep the Man from tracking him down.
- In Deponia Doomsday it's shown that a tinfoil hat stuffed with straw will provide Ripple Effect-Proof Memory necessary for a time traveler. Rufus, luckily, has a de facto built-in version thanks to a metal plate in his head.
- In Destroy All Humans!, you occasionally encounter humans wearing tinfoil hats. And Crypto can't read their minds.
- For the King has a headwear item called the Iron Foil Hat, which resembles a tinfoil hat in appearance and confers immunity to mind-related status effects such as stun, confuse, and frighten.
- L.A. Noire features a street mission in which Phelps has to chase down a tinfoil hat-wearing conspiracy theorist.
- In the second Special Operation for Marvel: Avengers Alliance, which introduced Emma Frost (one of the game's first truly psychic heroes), one of the random daily rewards was a Bauxite Interference Helmet, which could be used as in item to prevent psychic attacks on the character it was used on. Bauxite is the ore from which aluminum is extracted, making it a (very high-tech-looking) tinfoil hat.
- Some NetHack variants include these; wearing one blocks both incoming and outgoing telepathy.
- Phantom Doctrine: One of the bits of intel that you recover contains this conversation:
A: Bad news: [DELETED] has been field testing some CODA equipment, and a bunch of ham radio operators recorded the signal and called the cops.
B: Why is that a problem?
A: The police have been looking into the "sidewinders" affair — they might just connect the dots.
B: Then discredit those radio people in front of the cops — convince them we can control their brains with microwaves.
A: But that's exactly what we're doing!
B: Yeah. So exaggerate until it becomes implausible. Tell them a tinfoil hat could protect them or whatever.
A: Tinfoil hat? They'll never buy it.
- Dragon Age: Origins has a headwear item called the Conspirator's Foil, who's description is a clear-cut reference to this trope. The hat gives the wearer a boost to mental defenses, but lowers their social skills because "it causes observers to suspect you of paranoia."
- Dogen Boole in Psychonauts wears a tinfoil hat he claims prevents him from accidentally making people's heads explode with his Psychic Powers.
- Thimbleweed Park has a pirate hat wrapped in tinfoil. It doesn't protect against mind control, but it does reflect some real lasers used by the PillowTron AI. Chet, on of the characters in game, goes far further than a tinfoil hat: He tinfoils the entire inside of the giant novelty pizza costume he's wearing.
- 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.
- Karl from 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 Conversations and complaining about how crap their sex lives are. A Mind Is a Terrible Thing to Read indeed... It's not clear whether or not it works because their telepathic link uses radio waves or if it works because he thinks it ought to, but it makes him feel better.
- Deconstructed in Freeman's Mind, 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.
- In X-Ray & Vav, Rusty wears one as soon as he hears about The Corpirate's brainwashing ray, and it actually works
- In Freefall, Edge's protection from the lobotomizing program. Subverted in that in this case, since he is an AI and the program would be coming in on the com-net (basically wi-fi) since he has disabled all other means of communication except speech, aluminum foil covering his receiver would be enough to weaken or distort the signal enough to protect him from its effects.
- In The Greening Wars Hatchet's old "friend" Codex was wearing a tinfoil hat when they visited his bunker. But then again his former employers had put a tracking chip in his head.
- Questionable Content: Momo, normally excruciatingly polite, snarkily offers to make one for another AnthroPC. It Makes Sense in Context of the conversation.
- In Skin Horse, Jonah has the "attenuator", a colander with wires sticking out of it, which he believes is why he and Nera were unaffected when the Weirdness Censor suddenly went nationwide. (Other evidence, however, suggests that being regularly in contact with the weirdness increases your chance of not being affected somewhat anyway.)
- Saturday Morning Breakfast Cereal: Inverted in "Foil": It's not to protect him from the signals, it's to amplify them, since if there are such signals, they're probably very important.
- The 1st Membranes have tinfoil helmets as part of their standard gear. It helps block out the Warp from the Guards' minds.
- The Aluminum Foil Deflector Beanie.
- The "dear athetits" meme parodying excessively spurious claims to have disproven atheism — for whatever reason, its most iconic image is of a dog wearing a tinfoil hat.◊
- Episode 32 of Half in the Bag has a paranoid Jay surmise that Mr. Plinkett has become wise to his and Mike's schemes and placed a tracking beacon in their heads, and wears one of these to block it. The hat winds up interfering with a media satellite, causing Battleship and Dark Shadows to be downloaded directly into his brain. When Mr. Plinkett tries to download Ken Burns documentaries by wearing one of these, he gets a burst gamma radiation and becomes dumber.
- An episode of OutsideXtra had host Luke decking his baseball cap in tinfoil to prevent being possessed by Mario throwing his hat and possessing people. His co-host Ellen thinks that ridiculous, only for third co-host Andy to show up talking like Mario wearing the plumber's trademark hat. Ellen then steals the tinfoil hat so Luke can be possessed.
- 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. (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 Wild Mass Guessing section of This Very Wiki.
- Venetian Princess mentions wearing one in her The End Is Nigh (spoof of Lady Gaga's "You and I") to protect against solar flares.
- Subverted in Welcome to Night Vale: the Sheriff's Secret Police advise (through Cecil) that tinfoil hats are useless against mind-scanning helicopters, which could scan someone's brain even if they were behind twenty feet of lead. Mostly, the Secret Police are sick and tired of everyone believing this works and wearing such silly things in public.
Cecil: ... It draws unnecessary attention to yourself. It's pathetic and paranoid. The Secret Police are embarrassed for you.
- Whateley Universe: A Devisor, Dr. Herbolt, used his powers to make tin foil hats that blocked psychic intrusion, but because they are powered by his power, they might not work for anyone else. There's no info on that latter point.
- In The Amazing World of Gumball, Mr. Small wore this when he says he's aware of many things in Elmore disappearing like Janice. It turns out he was right when Gumball and Darwin noticed Molly was missing and they all went to the Void to rescue her and Janice. Tinfoil hats were worn so they are aware of the existence of the Void and at earlier times, change one's luck like in "The Helmet".
- In the Futurama movie "Into The Wild Green Yonder," Fry gains mind reading powers, and immediately gets bombarded with brain-chatter from everyone around him. A member of a secret society of mind-readers teaches him to wear a tin foil hat to block out other people's thoughts, and to keep other telepaths from reading his mind.
- A variation on this trope is used in Gravity Falls. In the episode "The Last Mabel Corn" it is revealed that Uncle Ford has lined his skull with metal to prevent the series antagonist Bill Cipher from possessing him or entering his mind without realizing it.
- A variant in Harvey Birdman, Attorney at Law: the cops arresting Mentok the Mindtaker wear helmets lined with aluminum as that blocks Mentok's mindtaking powers. Metal plates also block them, as he found out when he tried taking daredevil Ernie Devlin's mind.
- In "Olivia and Her Alien Brother" from Olivia, Olivia wears one and has her friend Julian do the same, under the mistaken impression that her "older bother" Ian is an alien studying intelligent life forms on Earth and plotting to get rid of all little sisters.
- On Regular Show, Mordecai and Rigby make foil hats when using Pops' '80s era cell phones, after he warned them that they cause tumors.
- Exaggerated 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.
- Being a paranoid cuckoo girl, Sticks of Sonic Boom inevitably references this in "My Fair Sticksy". She mentions one of her town defense system modes is meant to counter people trying to read her thoughts. According to her, it's a series of tinfoil-lined paddles to smack away telepathic signals. Or maybe just smack the mind readers themselves.
- In an episode of Stroker and 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.
- "CAT Scans" (properly called CT scans) are an incredible diagnostic tool for measuring changes in activity in the body, specifically the brain. But one class of people present a problem: those who for one reason or another have had restorative surgery involving replacement or reinforcement of bones with metal plates. The CT scan is ineffective for those who have had part of the skull replaced with a metal plate as this blocks the ability of the machine to observe brain activity in areas adjacent to the implant. So there may be a little Truth in Television operating here. But would even the most determined paranoiac have their entire skull replaced with metal? Read more here.
- One of the more ludicrous claims made by WW2 propaganda broadcaster Lord Haw Haw was that the British government was issuing hats made of very thin metal to protect against shrapnel from the Blitz. No doubt he was taken no more seriously at the time than other practitioners of this trope are now.
- The 1952 edition of Thrilling Wonder Stories advised readers worried about nuclear war to make cloaks of aluminium foil, "and you will be as safe as you can get. Aluminium reflects incredible amounts of heat, which is apparently the worst hazard if you are close to wear a bomb falls." Let's hope those Dirty Communists aren't using A-bombs in the megaton range, eh?