Parachute cord (also paracord or 550 cord) is a lightweight nylon kernmantle rope originally used in the suspension lines of US parachutes during World War II. Once in the field, paratroopers found this cord useful for many other tasks. It is now used as a general purpose utility cord by both military personnel and civilians. This versatile cord was even used by astronauts during STS-82, the 82nd
Space Shuttle mission, to repair the Hubble Space Telescope. The braided sheath has a high number of interwoven strands for its size, giving it a relatively smooth texture. The all-nylon construction makes paracord fairly elastic; depending on the application this can be either an asset or a liability. While the U.S. military has no overall diameter requirements in its specifications, in the field 550 cord typically measures 5⁄32 inch (4 mm) in diameter. The same properties which soldiers appreciate in paracord are also useful in civilian applications. After World War II parachute cord became available to civilians, first as military surplus and then as a common retail product from various surplus stores and websites. While some commercially available paracord is made to specification, even when labeled as such a given product may not correspond exactly to a specific military type and can be of differing construction, quality, color, or strength. Particularly poor quality examples may have significantly fewer strands in the sheath or core, cores constructed of bulk fiber rather than individual yarns, or include materials other than nylon. Paracord has also been used by many since the 1970s for whipmaking. The durability and versatility of this material has proved beneficial for performing whip crackers and enthusiasts. Since nylon does not rot or mildew, it has become known as an all-weather material for whipmaking. Hikers and other outdoor sports enthusiasts sometimes use "survival bracelets" made of several feet of paracord which is woven into a compact and wearable form. Such bracelets are meant to be unraveled when one needs rope for whatever purpose — securing cargo, lashing together poles, fixing broken straps or belts, assisting with water rescues, controlling bleeding with a tourniquet, etc. Additional uses for parachute cord are in the manufacture of items such as lanyards, belts, dog leashes, and key chains. This is becoming more popular as crafters are discovering this material.