A tin foil hat is a hat made from one or more sheets of aluminium foil (commonly called "tin foil" in the United States), or a piece of conventional headgear lined with foil, often worn in the belief or hope that it shields the brain from threats such as electromagnetic fields, mind control, and mind reading. The notion of wearing homemade headgear for such protection has become a popular stereotype and byword for paranoia, persecutory delusions, and belief in pseudoscience and conspiracy theories.
Some people – "Tin Foil Hatters" – have a belief that such hats prevent mind control by governments, spies, mobsters, corporations, or paranormal beings that employ ESP or the microwave auditory effect. People in many countries who believe they are "targeted individuals", subject to government, corporate, or criminal spying or harassment, have developed websites, conference calls, and support meetings to discuss their concerns, including the idea of protective headgear. Vice Magazine wrote that the tin foil hat in popular culture "can be traced back in a very weird and prescient short story written in 1927 by Julian Huxley" titled The Tissue-Culture King, wherein the main character uses a metal hat to prevent being mind controlled by the villain scientist. Over time the term "tin foil hat" has become associated with paranoia and conspiracy theories.
Effects of strong electromagnetic radiation on health have been documented for quite some time. The efficiency of a metal enclosure in blocking electromagnetic radiation depends on the thickness of the foil, as dictated by the "skin depth" of the conductor for a particular wave frequency range of the radiation. For half-millimetre-thick aluminum foil, radiation above about 20 kHz (i.e., including both AM and FM bands) would be partially blocked, although aluminum foil is not sold in this thickness, so numerous layers of foil would be required to achieve this effect.
A belief also exists that aluminum foil is a protective measure against the effects of electromagnetic radiation (EMR) for many unspecified EMR frequencies. There are some allegations that EMR exposure has negative health consequences.
In 1962, Allan H. Frey discovered that the microwave auditory effect (i.e., the reception of the induced sounds by radio-frequency electromagnetic signals heard as clicks and buzzes) can be blocked by a patch of wire mesh (rather than foil) placed above the temporal lobe.
In 2005, a tongue-in-cheek experimental study by a group of MIT students found that tin foil hats do shield their wearers from radio waves over most of the tested spectrum, but amplified certain frequencies, around 2.6 GHz and 1.2 GHz.
In popular cultureEdit
In 2005, Bruce Perens reported on an encounter between Richard Stallman and security personnel at the UN World Summit on the Information Society, titled, "Friday, November 18: Richard Stallman Gets in Trouble with UN Security for Wearing a Tin-Foil Hat". 18 November 2005.. The tin-foil hat in the title was figurative, as Stallman did not actually devise a tin-foil hat, but instead wrapped an identification card containing an Radio-frequencey identifiction device in tin foil in protest against the intrusion on his privacy. The incident was widely reported, and the image of a tin-foil-hat-wearing oddball entered popular culture, as the wider audience was not generally aware of the ramifications of the new technology.
In 2014, "Weird Al" Yankovic parodied the song "Royals" by Lorde on his album Mandatory Fun, reworking it to "Foil". The song begins as a parody of an infomercial, advising viewers about the benefits of aluminum foil before descending into conspiracy theories including the Illuminati's New World Order and alleging the moon landing was faked. During the last chorus, Weird Al claims a tin foil hat will protect the viewer from alien mind control.
In a 2016 article, the musician and researcher Daniel Wilson writing in paranormal magazine Fortean Times noted an early allusion to an "insulative electrical contrivance encircling the head during thought" in the unusual 1909 non-fiction publication Atomic Consciousness by self-proclaimed "seer" John Palfrey (aka "James Bathurst") who believed such headgear was not effective for his "retention of thoughts and ideas" against a supposed "telepathic impactive impingement".
The book series Artemis Fowl by Eoin Colfer features a paranoid centaur character named Foaly, who wears a tin-foil hat to protect from mind-readers. The novel Idiots in the Machine by Edward Savio portrays a character who believes tin foil keeps harmful gamma rays away, becoming a media sensation after marketing a successful line of foil hats to Chicago.
The 2019 HBO television series Watchmen features the character Wade Tillman/Looking Glass, a police officer who wears a mask made of reflective foil, and while off-duty, a cap lined in foil to protect his mind from alien psychic attacks.
Though not specifically involving a tin foil hat, Chuck McGill (the older brother of James McGill, aka Saul Goodman in "Better Call Saul") claims to have electromagnetic hypersensitivity, leading him to insulating himself using space blankets. 
In 2022, anti-vaccination protesters in Wellington, New Zealand were seen wearing tinfoil hats, in a mistaken belief that their illnesses – possibly COVID-19 – were being caused by electromagnetic rays fired at them by the Government.
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- "A Brief Cultural History of the Tin Foil Hat". Vice.com. Retrieved 9 March 2021.
- Huxley, Julian. "The Tissue-Culture King". Retrieved 9 March 2021.
- Huxley, Julian (August 1927). "The Tissue-Culture King". Amazing Stories.
Well, we had discovered that metal was relatively impervious to the telepathic effect, and had prepared for ourselves a sort of tin pulpit, behind which we could stand while conducting experiments. This, combined with caps of metal foil, enormously reduced the effects on ourselves.
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- Soniak, Matt (28 September 2012). "Tin Foil Hats Actually Make it Easier for the Government to Track Your Thoughts". The Atlantic. Retrieved 4 August 2020.
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- Bathurst, James (1909). Atomic Consciousness Abridgement. W. Manning, London.
- Wilson, Daniel (June 2016). "Atomic-Consciousness". Fortean Times.
- Lang, Cady (20 September 2019). "Area 51 Raid But Make It Fashion: It Takes a Lot to Stand Out at Alien-Themed Festival But This Guy's Tin Foil Hat Is Working". Time. Retrieved 10 March 2020.
- Whittaker, Richard (9 July 2017). "DVDanger: Don't Knock Twice". The Austin Chronicle. Retrieved 14 April 2020.
- Miller III, Randy (1 February 2009). "Futurama: Into The Wild Green Yonder". DVD Talk. Retrieved 10 March 2020.
- Erdmann, Kevin (18 November 2019). "Watchmen: Biggest Comic Easter Eggs in Episode 5". Screen Rant. Retrieved 10 March 2020.
- "Better Call Saul: Is electromagnetic hypersensitivity a real health risk?". TheGuardian.com. 15 February 2015.
- "Anti-mandate protesters making tinfoil hats amid fears radiation, not COVID-19, is causing illness at camp". Newshub. Retrieved 25 February 2022.
- Media related to Tin foil hats at Wikimedia Commons