Signs, Tins

A tin-foil hat or aluminium foil deflector beanie is a piece of headgear made from one or more sheets of aluminium foil or similar material. more...

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Some people wear the hats in the belief that they act to shield the brain from such influences as electromagnetic fields, or against alien interference mind control and/or mind reading.

The concept of wearing a tinfoil hat for protection from such threats has become a popular stereotype and term of derision. The phrase serves as a byword for paranoia and is often used to characterize conspiracy theorists.

Tin-foil hats and paranoia

There have been some reports of people who believe in the efficacy of tin-foil hats and similar devices. Reasons for use include preventing perceived harassment from paranormal beings or stopping the experience of hearing voices in one's head. Also the belief that the foil deflects mind control signals from project HAARP that allegedly transmits signals from mobile phone towers. These draw on the stereotypical images of mind control operating by ESP or technological means, like microwave radiation. Belief in the effectiveness of tin-foil hats is popularly linked to mental illnesses such as paranoid schizophrenia.

Scientific basis

The belief that a tin-foil hat can significantly reduce the intensity of incident RF radiation on the wearer's brain is not completely without a basis in scientific fact. A well constructed tin-foil enclosure would approximate a Faraday cage, reducing the amount of radiofrequency electromagnetic radiation entering from outside. 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 as electromagnetic shielding for 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. 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 belongs properly to the realm of pseudoscience.

Read more at Wikipedia.org