This specification covers the general requirements for materials used in rubber seals of concentrating solar collectors. Design requirement pertains only to permissible deflections of the rubber during thermal expansion or contraction of the seal in use and the tolerances in dimensions of molded and extruded seals. The materials shall be classified according to usage: Type C and Type W; according to degrees of hardness: Grade 2; 3; 4; 5; 6; 7; and 8. The seals shall be classified as: Class PS and Class SC. Desert outdoor exposure and xenon arc laboratory exposure shall be performed to determine the resistance to solar radiation. The following test methods shall be performed: ultimate elongation; compression set; resistance to heating; resistance to ozone; resistance to low temperature; and adhesion loss.