Tin foil hat

A tin foil hat is a hat made from one or more sheets of aluminium foil, 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.
"Tin foil" is a common misnomer for aluminium foil; packaging metal foil was formerly made out of tin before it was replaced with aluminium.
Origin.
Some people have a belief that such hats prevent mind control by governments, spies, or paranormal beings that employ ESP or the microwave auditory effect. People in many countries who believe they are "targeted individuals", subject to government spying or harassment, have developed websites, conference calls, and support meetings to discuss their concerns, including the idea of protective headgear. "Vice Magazine" claimed that the tinfoil hat in popular culture "can be traced back in a very weird and prescient short story written in 1927 by Julian Huxley, brother of the better-known author Aldous and half-brother to Nobel laureate Andrew" 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.
Scientific basis.
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 culture.
In 2014, "Weird Al" Yankovic parodied the song "Royals" by Lorde on his album "Mandatory Fun", reworking it to "Foil". The song references conspiracy theories such as the Illuminati and the New World Order, and Weird Al wears a tinfoil hat in the video.
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". 
Tin foil hats have appeared in such films as "Signs" (2002), ' (2005), and ' (2009).
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.
In Brandon Sanderson's Mistborn series, aluminum foil hats block magical emotion manipulation.
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.
Other uses.
In 2020, an Uzbekistani citizen tried to cross the Belarusian-Lithuanian border illegally using aluminum foil padding of the attire and a tin foil hat, to avoid detection by thermographic cameras. It was reported that the border guards face similar violations quite regularly.