In my 8 years as an online civil liberties writer, I’ve heard a lot of conspiracy theories—but I’ve never actually met anyone who claims to wear a tinfoil hat. In theory, they keep out secret mind surveillance/mind control rays. In practice, well…I’ve never actually encountered anyone who falls under the heading of “in practice." When “Weird Al" Yankovic had fun with the idea last week (in his parody of Lorde’s “Royals”), we all got the reference, and it was clever:
Where did all of this start? Most sources trace the idea to Julian Huxley’s “The Tissue-Culture King,” a dystopian short story published in the August 1927 issue of Amazing Stories, where our narrator avoids falling under the power of a mind control device by disrupting its waves with metal foil:
“[W]e 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."
There’s also a comic book example: Magneto, archfoe of the X-Men, shuts out Professor X’s telepathic abilities by wearing a metal helmet. But outside of fiction, you’re not going to find many people who actually wear, or at least admit to wearing, a metal hat to keep out telepathic devices.
Huxley was an accomplished scientist, so we can reasonably presume he was familiar enough with the work of Michael Faraday to postulate that the pulpit and/or foil hat might function as a Faraday cage, diffusing the telepathic waves before they could reach the brain. That may well have worked for Huxley's hypothetical device, but it wouldn't do a good job of deflecting modern-day technology; a 2005 study found that wearing a tinfoil hat actually amplifies cellular and satellite radio waves.