shapes. Isostatic shapes have isotropic physical properties, whereas direct formed and compression molded shapes exhibit anisotropic physical properties. Some examples of standard polyimide compounds are: SP-1 virgin polyimide provides operating temperatures from cryogenic to 300 °C (570 °F), high plasma resistance, as well as a UL rating for minimal electrical and thermal conductivity. This is the unfilled base polyimide resin. It also provides high physical strength and maximal elongation, and the best electrical and thermal insulation values. Example: Vespel SP-1. 15% graphite by weight, SP-21 added to the base resin for increased wear resistance and reduced friction in applications such as plain bearings, thrust washers, seal rings, slide blocks and other wear applications. This compound has the best mechanical properties of the graphite-filled grades, but lower than the virgin grade. Example: Vespel SP-21. 40% graphite by weight, SP-22 for enhanced wear resistance, lower friction, improved dimensional stability (low coefficient of thermal expansion), and stability against oxidation. Example: Vespel SP-22. 10% PTFE and 15% graphite by weight, SP-211 added to the base resin for the lowest coefficient of friction over a wide range of operating conditions. It also has excellent wear resistance up to 149 °C (300 °F). Typical applications include sliding or linear bearings as well as many wear and friction uses listed above. Example: Vespel SP-211. 15% moly-filled (molybdenum disulfide solid lubricant), SP-3 for wear and friction resistance in vacuum and other moisture-free environments where graphite actually becomes abrasive. Typical applications include seals, plain bearings, gears, and other wear surfaces in outer space, ultra-high vacuum or dry gas applications. Example: Vespel SP-3. Material properties data References Plastics DuPont products