 Bungee cord

A bungee cord (sometimes spelled bungie), also known as a shock cord - and in Australia, an occy strap, octopus strap or jockey strap - 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 spiralling 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.