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NEMA grade G7 Glass-Cloth Reinforced Silicone - natural color is typically cream to white. Composed of a continuous glass woven cloth base impregnated with a silicone resin binder, this grade has excellent heat and arc resistance. (Silicone thermosetting resins are among the best of all polymer materials in resistance to temperature. Hence, silicone is broadly used for high temperature electronic applications requiring low electrical losses. Silicone is not as strong as epoxies and phenolics upon aging at lower temperatures but is stronger upon aging over 400°F/204°C.) G7 has extremely good dielectric loss properties under dry conditions and good electrical properties under humid conditions, although the percentage of change is high.
Polyester Grades of Industrial Laminates
NEMA grade Glass-Mat Reinforced Polyester - GPO-1 (tan color), GPO-2 (red color), and GPO-3 (red color). These grades are composed of random mat (non-woven) fiberglass reinforcement held together by a polyester resin binder. (Polyesters are versatile resins, which handle much like epoxies. Of course, the basic resins are chemically different. It is their physical application forms, which make them similar. Despite lower costs, the important disadvantages of polyesters, as compared with epoxies, is lower adhesion to most substrates, higher polymerization shrinkage, and a greater tendency to crack during cure or in thermal shock and greater change of electrical properties in a humid environment.) GPO-2 offers superior arc resistance over GPO-1, while GPO-3 offers both arc and track resistance.
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