Shock Cord consists of a braided jacket of a textile fiber such as nylon, polypropylene or polyester. This braided jacket is tightly braided over a core of rubber. When the shock cord is stretched, the braided jacket actually flexes and actually compresses the rubber fibers in the core, so not only does the rubber core stretch, it is also compresses laterally as the braided jacket constricts around it.
Natural rubber is found in most common shock cord and nylon is one of the more common fibers for the braided jacket. Polypropylene is used in less expensive shock cord and has a tendency to develop breaks and holes in the braided jacket, due to the fact that polypropylene does not have the tensile strength or abrasion resistance that nylon has.
Most shock cord stretches from 50% to 80% of it’s original, un-stretched length.
Elastic Webbing is similar to shock cord in operating principle, but it is a woven or knitted textile product that has a flat or linear construction. There are two main varieties of Elastic Webbing, Knitted and Woven. Knitted Elastic has a distinctive ribbing that runs lengthwise along the material. Whereas woven elastic webbing has a smoother appearence with a weave that produces a diagonal pattern that is less pronounced than the ribbing in the knitted elastic. The edges of Woven elastic are also noticably thinner than the center of the material. This thin edge is usually 1/16” to 1/8” wide on both sides of the material.
There is not much difference in durability or strength between woven and knitted elastic webbing, however smaller widths of elastic are more likely to be knitted, and wider widths, wider than 3/4” are typically woven instead of knitted.
Elastic is commonly used to manufacture straps that need to stretch or have a tension to accomodate an object that typically changes sizes and/or flexes frequentl, where a strap of a fixed size would become too tight ot too lose in the course of the movement or flux. Elastic is often used in conjuction with webbing, or webbing hardware.