A tin-foil hat, also tinfoil hat, is a piece of headgear worn by some in the belief that it protects the brain from such influences as electromagnetic fields, or as a shield against mind control and/or mind reading. Hats made from foil are very rarely used, since the injuries they might guard against are highly speculative, and their effectiveness in preventing such harm would be dubious even if the danger were plausible. Instead, the concept has become a popular stereotype and term of derision; in Internet culture, the phrase (sometimes as the abbreviation "TFH") serves as a byword for paranoia.

Tin-foil hats and mental illness

There have been some people who believe in the actual utility of tin-foil hats and similar devices. Reasons for use include preventing abduction by alien beings, or stopping unpleasant experiences such as hearing voices in one's head. This draws on the stereotypical image of mind control operating by means of ESP, microwave radiation or other technological means. In some cases, belief in tin-foil hats could be a manifestation of a disorder such as paranoid schizophrenia.

The delusion of "mind control rays" or other invasive mental activity may seem very real to those afflicted with severe paranoid delusions, and such persons have been known to make and wear improvised defences against the imagined invasion. A placebo effect may even convince the sufferer that the device actually works. While aluminium foil or tin-foil is traditional, less fragile materials such as 3M Velostat (a kind of metallised plastic) and metal window-screen mesh are now more commonly used. Electrical conductivity is seen as a key quality.

There is a small amount of truth or reason to be found in the tin-foil hat story. A well constructed tin-foil enclosure would approximate a Faraday cage, reducing the amount of (notionally harmless) radiofrequency electromagnetic radiation inside. A common high school physics demonstration involves placing an AM radio on tinfoil, and then covering the radio with a metal bucket. This leads to a noticeable reduction in signal strength. The efficiency of such an enclosure in blocking such radiation depends on the thickness of the tin-foil, as dictated by the skin depth, the distance the radiation can propagate in a particular non-ideal conductor. For half-millimeter-thick tin-foil, radiation above about 20 kHz (i.e., including both AM and FM bands) would be partially blocked. The effectiveness of the tin-foil hat in stopping radio waves is greatly reduced by the fact that it is not a complete enclosure. Placing an AM radio under a metal bucket without a conductive layer underneath demonstrates the relative ineffectiveness of such a setup. Indeed, because the effect of an ungrounded Faraday cage is to partially reflect the incident radiation, a radio wave that is incident on the inner surface of the hat (i.e., coming from underneath the hat-wearer) would be reflected and partially 'focused' towards the user's brain. While tin-foil hats may have originated in some understanding of the Faraday cage effect, the use of such a hat to attenuate radio waves belong properly to the realm of pseudoscience.

Tin-foil hats in pop culture

• The paranoid centaur Foaly, in Eoin Colfer's Artemis Fowl series of books, wears a tin-foil hat to protect from mind-readers.
• In an episode of The Simpsons, Bart (while paranoid under the influence of a drug to cure hyperactivity called "Focusin") wears a tin-foil hat.
• In the film Lovesick, Dudley Moore plays a psychiatrist who gives a homeless patient some aluminum foil to "protect" the patient from the "mind control rays" his patient claims are bombarding him.
• In Total Recall, the hero (Douglas Quaid, played by Arnold Schwarzenegger) wraps a wet towel around his head to stop outgoing radiowaves from a transmitter inside his head.
• In Signs, the children and younger brother of the lead character wear tin-foil hats to prevent their minds from being read. This is parodied in Scary Movie 3, in which the tin-foil hats are actually giant Hershey's Kisses
• In the X-Men movies, Magneto wears a helmet that prevents Stryker's son (in X2) and Professor X (in X-Men and X2) from using telepathy against him.
• Former Marvel Comics supervillain Juggernaut has worn a helmet of mystical alloy as protection against use of telepathy.
• Tin-foil hats are often referenced on Internet forums such as Slashdot.
• In his autobiography, Frank Zappa refers to Echo Park residents "Crazy Jerry," an electricity addict and speed user who had been institutionalized a number of times, and his roommate known only as "Wild Bill the Mannequin Fucker," a chemist and methamphetamine cook who modified department store mannequines for sexual uses. Both are reputed to have employed metallic hats (vegetable steamers, aluminum pots, tin-foil etc.,) to "keep people from reading their minds." Zappa once recorded Crazy Jerry's life story, excerpts of which can be heard on some of his early recordings.

See also

• User:Antaeus Feldspar
• Frey effect
• List of hats and headgear
• Microwave auditory effect
• Tinfoil Hat Linux
• Homokaasu
• James Tilly Matthews
• Slashdot subculture

External links

• Do tinfoil helmets provide adequate protection against mind control rays? – from The Straight Dope (registered trademark of Chicago Reader, Inc.)
• Stop Alien Abductions – instructions for making a "thought screen helmet" from 3M Velostat
• Aluminum Foil Deflector Beanie – parody
• Pet Foil Hat Technology – parody
• Tinfoil Hat Linux– ultra-secure Linux distribution