[ tin-foil ]
/ ˈtɪnˌfɔɪl /
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tin, or an alloy of tin and lead, in the form of a thin sheet, much used as a wrapping for drugs, foods, tobacco, etc.
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Also called, British, silver paper.

Origin of tinfoil

First recorded in 1425–75, tinfoil is from the late Middle English word tynfoile.See tin, foil2
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2023


What is a tinfoil hat?

Tinfoil hat is a shorthand for saying someone believes in conspiracy theories, is paranoid, or is crazy more generally.

Where did the term tinfoil hat come from?

In the 19th century, a tinfoil hat was a kind of party hat. The phrase took a turn, though, in the 20th century. A 1920s sci-fi short story, “The Tissue-Culture King” by Julian Huxley, featured characters wearing “caps of metal foil” to evade mind-control waves.

Huxley’s headwear illustrates the core concept of the tinfoil hat: it acts as a kind of Faraday cage to block various kinds of electromagnetic waves. We can find the specific phrase tinfoil hat in the 1980s, by which time it had become associated with individuals who would wear them in the belief they would protect them from nefarious rays seeking to surveil, brainwash, or otherwise influence them.

In the 1980–90s, tinfoil hat became a shorthand for a “conspiracy theorist”—you know, JFK, moon landing, and later, 9/11 truthers. A 1997 internet commenter observed that tinfoil hat was “the oldest insult” on Usenet.

Nevertheless, the tinfoil hat became a full-fledged trope in popular media in the 1990s–2000s. In a 1999 episode of The Simpsons, Bart becomes a paranoid conspiracy theorist wearing a tinfoil hat because he fears Major League Baseball was spying on everyone. Spoiler alert: He was right.

In the 2002 film Signs, Mel Gibson’s character and his family don tinfoil hats to keep aliens from reading their minds. In the late 1990s and 2000s, the cartoon Futurama regularly featured a tinfoil hat-wearing character with some really far-out—veritably cosmic—prophecies.

Musician Weird Al included a verse riffing on tinfoil hats and conspiracy theories in his 2014 parody song of Lorde’s “Royals,” called “FOIL.”  In a 2015 episode of the TV show Better Call Saul, a character wraps himself in space blankets to shield him from electromagnetic radiation; he’s threatened with being committed to a mental hospital.

How to use the term tinfoil hat

Tinfoil hat is widely used as an insult for acting crazy or believing in nonsense or “out-there” ideas, including conspiracy theories.

People who suffer from genuine mental illnesses, such as schizophrenia, have discussed wearing actual tinfoil hats when dealing with intrusive thoughts and hallucinations. A 2005 study showed, though, that a tinfoil hat actually amplifies radio frequencies instead of blocking them.

More examples of tinfoil hat:

“Study finds conspiracy theories aren’t all spread by tinfoil-hat-wearing crazies”
RT (headline), April 2018


This content is not meant to be a formal definition of this term. Rather, it is an informal summary that seeks to provide supplemental information and context important to know or keep in mind about the term’s history, meaning, and usage.

How to use tinfoil in a sentence

British Dictionary definitions for tinfoil

/ (ˈtɪnˌfɔɪl) /

thin foil made of tin or an alloy of tin and lead
thin foil made of aluminium; used for wrapping foodstuffs
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012