The term tin foil hat is generally used as a derogatory remark toward someone advancing a conspiracy theory or other story that is considered incredible. It appears to have been coined to describe people who claimed UFO sightings or claimed to have been previously abducted by aliens. It was suggested that such a person might wear a tin foil hat in order to keep aliens from intercepting his or her brainwaves. However, there are some people that actually construct tin foil hats, believing they will protect against mind control programs, radio waves, and electromagnetic radiation (EMR).

In fact, a type of device made from aluminum or tin foil may help reduce EMR. It isn’t foolproof since hats or other protective gear aren't solid enough structures. Electromagnetic radiation is also said not to be harmful, despite earlier possible concerns.

Some people also say that those who promote conspiracy theories or government conspiracies are part of a tin foil hat brigade, or a tin foil hat group. Those alleged to be a part of such a group may or may not believe that a tin foil hat is useful. Anyone that actually does wear a tin foil hat is usually considered to be disturbed. Yet, the term is most often used to ridicule people, even those who would never consider wearing accessories made from Reynolds Wrap®. The wilder the conspiracy theory, the more likely the term is to be used.

Many times, when debates arise over various conspiracy theories, tin foil hat comments are used to discredit the person attempting to advance some cover up or other questionable act by a government. On political message boards people say things like, “I see you’re wearing your tin foil hat,” to show that they think the theory has no basis and that the person suggesting it is simply paranoid. It can also be used in a self-deprecating way such as in saying, “I know you’ll think I’m wearing a tin foil hat, but I believe this conspiracy is real.”

A tin foil hat may also be known as an aluminum foil helmet. Studies have been done to test their effectiveness, although such studies are often not given much credibility. There are also people that will sell you a tin foil hat. Check online for tin foil hat sellers. A tin foil hat might just make a good gag gift if given in the spirit of fun.