Stefans are usually made from foam backer rod (also known as caulk saver) and a weight. Common weights include #6 washers, copper BB's, 1/4" slingshot weights, molded silicone tips, or sometimes putty or another non-hardening substance. The top is then covered with a piece foam, felt, hot glue dome, or rubber tip. The result is a straight flying, accurate, faster, longer range, and cheaper dart; the only downside to Stefans are that they are slightly more painful.
The most popular and well-organized Nerf wars require that their Stefans have a felt or softer cover for safety purposes. Understandably, Stefans are one of the reasons why protective eyewear is always a must. With skill, someone can easily make hundreds of Stefans for a low cost.
Some blasters are unable to fire Stefans in their stock form. This is most likely due to an air restrictor peg which must be removed before Stefans can be used. Certain blasters which lack true barrels such as the SuperMAXX 350 and Air Tech 1000 are incapable of firing Stefans without a complete barrel swap.
Recently, the term "Stefan dart" has been used to describe short length darts. This term has been widely accepted by the Nerf community to describe darts that are different than Streamline Darts. The company Xplorer has been calling short darts Stefans since 2010, which has been accepted by the majority of Nerf enthusiasts.