It has long been a joke that if you want to prevent the government from reading your mind, you wear a “tin foil hat.” The practice actually dates back to the early days of radio, when people believed that the government could use radio waves to read their thoughts. To prevent this, they would wear headgear made of aluminum foil. Of course, we now know that the government can’t read our thoughts through radio waves, though it’s likely they read our emails. The joke, however, appears to be on us, as there seems to be a scientific basis for believing that foil can do some blocking. In fact, the effects of strong electromagnetic radiation on health has been documented for quite some time. The efficiency of a metal enclosure in blocking electromagnetic radiation depends on the thickness of the foil. For ½mm-thick aluminum foil, radiation above about 20 kHz would be partially blocked, although foil is not sold in that thickness. Thus, you’d have to use several layers of foil to achieve the effect. In 2005, a tongue-in-cheek experiment performed by a group of MIT students found that foil hats do shield wearers from radio waves over most of the tested spectrum. So, the next time you hear someone say that they’re wearing a tin foil hat, they just might be onto something.
