Manufacturers make bungee cord from usually either natural or synthetic rubber. Natural rubber, also called latex rubber, can be extended in its shape and has high resilience. It also regains its original shape well after being stretched, called tensile strength. Standard bungee cords come in diameters ranging from 1/4 inch to over 3/5 inch. Their lengths vary from a few inches to 6 feet for trucking industries. Most cords are covered in a cotton or nylon sheath for protection. Cords sold at department, hardware and auto stores feature various sizes, with either J-shaped or S-shaped hooks on the ends. The cords can be stretched usually over twice their length, and can be attached to other cords for additional length. This gives them versatility and ease when holding items in place for moving or storage.
Bungee cords used for bungee jumping come in two basic designs. Some jumpers prefer mil-spec cords, the original design used for most everyday-use bungee cords. Mil-spec cords range in diameter from .25 inch to .87 inch. Their lengths vary greatly and can be as long as 200 feet. The U.S. military designed mil-spec cords to hold down tanks on boats and planes. They designed nylon or cotton sheath to protect the cord from moisture and dirt. Bungee jumpers use mil-cord bungee for its increased safety and tighter stretch. Generally, manufacturers bundle 3 to 6 cords 5/8 inch in diameter together for jumping. Each cord provides a minimum breaking strength of 1,500 lbs. Others prefer Euro cords for their greater stretch. Some Euro cords made in New Zealand stretch 200 to 300 percent their length, usually 100 to 200 feet. The all-rubber cords come from more than 1,000 individual strands of rubber tied together to make a solid cord. These cords come without the protective sheath. However, some prefer this because after each jump, the rubber, left uncovered, can easily be inspected for wear or damage.
Manufacturing Bungee Cords
Manufacturing bungee cords begins with preparing and extruding long ribbons of natural or synthetic rubber. The ribbons measure .09 to .12 inches thick, .25 inch wide and up to 100 feet long. When the rubber ribbons cool they are coiled together and shipped to a bungee cord manufacturer. The more ribbons or strands branded together gives greater diameter and strength to the bungee cord. A machine called a braider combines the strands, and also weaves the covering yarn around the rubber bundle in standard and mil-spec cords.
Bungee Safety Concerns
Bungee jumping has obvious safety concerns. Snapping from the force of jumping can occur, and protective harnesses can be attached incorrectly. However, injuries often occur from everyday bungee cords. When stretching the cords for holding items in place, energy builds up and can suddenly be released if an end is let go or not attached well. Bungee cords travel up to 60 mph when released, and cause injuries each year, especially to the eye. Each year, according to one hospital study, more than half of eye injuries caused by bungee cords required hospitalization. Loss of vision and even the eye itself occurs each year. Wearing protective eye gear and not over-stretching the bungee cords can help prevent injury.