If FEP Teflon* and Silicone Rubber insulated products both are rated for 200 C continuous duty, what is the difference? How do you determine which is the best material for a given application? FEP Teflon is a thermoplastic. This means that each time it is exposed to sufficient heat, it will re-melt and flow. Silicone rubber is a thermoset that has been cured with a heat-activated catalyst to form stronger chemical bonds throughout its molecular structure. When exposed to excessively high temperatures, the rubber will simply char or degrade to a very dense ash. This fundamental difference can be very meaningful in applications where exposure of the insulation to extreme temperatures or fire is common. A plastic insulation may melt or drip inside the conduit or cable tray or on the structure and equipment below, that results in costly cleanup or replacement. The silicone rubber material by contrast will simply char, and may be removed cleanly for easy replacement. Teflon is a much harder material than silicone rubber, having an ultimate tensile strength of about 2,450 psi compared with SR, which has an ultimate tensile of about 1200 psi. This difference is the reason why most products insulated with silicone rubber also have a fibrous braid covering over the outer surface. The braid provides resistance to cuts and abrasion. The FEP Teflon is both hard and stiff. Once the insulation is wound upon a reel, for example, it will continue to retain the shape of the package it was placed on and unwind in "loops." Silicone rubber by contrast remains extremely pliable and retains no "memory" of the shape it was formed to last. This inherent flexibility makes it an excellent choice for cable that travels (that are repeatedly bent and flexed) in their application. Electrically, both of these materials provide excellent insulation. For transmission of high frequency alternating current signals, however, the FEP Teflon is much more effective. This is because the FEP may be applied with minimal wall thickness. This allows for less resistance to the passage of the signal, resulting in higher transmission rates and longer effective transmission distances without amplification. The silicone rubber, by contrast, can retain a capacitive charge for extremely long periods of time. The comparative resistance to moisture is also worth mentioning. FEP Teflon is impervious to moisture; it will not absorb water or pass it through even a thin layer. Silicone rubber, like many electrical insulation materials, will absorb small amounts of water that may actually pass through the insulation to the materials underneath.

NOTE: * Teflon is a registered trademark of E.I. DuPont de Nemours & Company.