NEMA grade XX  Paper Reinforced Phenolic -- natural color is typically light tan to brown. This  grades is composed of a paper base impregnated with a phenolic resin binder. (Phenolics are the oldest, best-known general purpose thermoset resins. They are among the lowest in cost and easiest to process. Phenolics are quite adequate for a fair percentage of electrical applications. Generally speaking, they are not equivalent to epoxies in resistance to moisture, humidity, dimensional stability, shrinkage and retention of electrical properties in extreme environments.) The paper reinforced phenolic has good electric strength properties with fair mechanical strength and are outstanding for use as template material and/or back-up material. 

 XX MIL-I-24768/11 PBG, IEC 60893-3 Type 4 PF CP 203