Their results indicated that the predominant reaction contributing to compression set was oxidative degradation of the rubber. The degradation process leading to the compression set was oxidative crosslinking in nature. Additionally, the solvent swell tests showed a correlation between the compression set and crosslink density (CLD). Chang7 investigated the effect of changing Mooney viscosity on the hardness, elongation at break, and compression set of a sulfur-cured NBR rubber and reported reduction in the compression set as the Mooney viscosity was increased. Evidently, the compression set of NBR was influenced by many factors.