Specific gravity is a nondestructive test used as a quality control check of the consistency of formulation and processing of brake lining. Specific gravity alone shows nothing about a lining's ability to develop friction or to resist fade when used as a friction element in brakes. Specific gravity varies with the formulation of the lining.
The specific gravity of sintered metal powder linings, particularly those which have steel backing members, is usually determined somewhat differently. Reference ASTM B 376. The specific gravity and the range of specific gravity are peculiar to each formulation and, therefore, the acceptable values or range must be established for each formulation by the manufacturer.