CHAPTER 6 Transmission Techniques: Wire and Cable themselves be ground up and turned back into wire insulation, or many other uses. The term thermo- plastic means changed by heat and is the source of the common term plastic. Rubber compounds, on the other hand, are thermoset. That is, once they are made, they are set, and the process cannot be reversed. Rubber, and its family, is cured in a process sometimes called vulcan- izing. These compounds cannot be ground up and recycled into new products. There are natural rub- ber compounds (such as latex-based rubber) and artificial, chemical-based rubber compounds such as EPDM (ethylenepropylene-diene monomer). The vast majority of wire and cable insulations are plastic-based compounds. Rubber, while it is extremely rugged, is considerably more expensive than most plastics, so there are fewer and fewer manufacturers offering rubber-based products. These materials, both rubber and plastic, are used in two applications with cable. The first application is insulation of the conductor(s) inside the cable. The second is as a jacket material to protect the contents of the cable. JACKETS The jacket characteristics of cable have a large effect on its ruggedness and the effect of environment. A key consideration is often flexibility, especially at low temperatures. Audio and broadcast cables are manufac- tured in a wide selection of standard jacketing materials. Special compounds and variations of standard compounds are used to meet critical audio and broadcast application requirements and unusual environ- mental conditions. Proper matching of cable jackets to their working environment can prevent deterior- ation due to intense heat and cold, sunlight, mechanical abuse, impact, and crowd or vehicle traffic.