A larger variant of the skullcap, the beanies were a working hat associated with blue collar laborers, welders, mechanics, and other tradesmen who needed to keep their hair back but for whom a brim would be an unnecessary obstruction. Beanies do sometimes have a very small brim, less than an inch deep, around the brow front. The baseball cap evolved from this kind of beanie, with the addition of a brim to block the sun.
In the late 1940s, science fiction fanzine artist Ray Nelson (himself still in high school) adopted the use of the propeller beanie as emblematic shorthand for science fiction fandom, in self-mockery of the popular image of fans as childish and concerned with ephemera (i.e., science fiction); references to it are ironically now used to identify old-fashioned fans, as opposed to more modern fans of media SF. The propeller beanie increased in popular use through comics, and eventually made its way onto the character of Beany Boy of "Beany and Cecil." Today, computer savvy and other technically proficient people are sometimes pejoratively referred to as propeller heads thanks to the one-time popularity of the propeller beanie hats.
In the early 1990s, the beanie saw a reemergence in popularity due to the "grunge" clothing trend as well as the popularization of snowboarding and other cold weather sports activities. The modern beanie is usually made of fleece, or special synthetic material that wicks moisture away.