Bungee Cord

A bungee cord (sometimes spelled bungie), also known as a shock cord, is an elastic cord composed of one or more elastic strands forming a core, usually covered in a woven cotton or polypropylene sheath. The sheath does not materially extend elastically, but it is braided with its strands spiraling around the core so that a longitudinal pull causes it to squeeze the core, transmitting the core's elastic compression to the longitudinal extension of the sheath and cord.