As detailed in ASTM D 2632, resilience (also known as rebound) refers to a compound’s ability to regain its original size and shape after temporary deformation. Resilience testing typically involves the dropping of a small weight onto a test specimen (such as a compression set button, see Figure 27). The extent to which the weight bounces back is then noted as a percentage of the initial drop height. A highly resilient material (one that can rapidly regain its dimensions) might engender a 70% rebound value, but values in the range of 40 to 50% are more typical for the majority of elastomers tested. Though compounding may improve an elastomer in this area, it can also detract from good resilience, which is largely an inherent property. As a general rule, resilience is most critical in dynamic seals.

As important as they are, the physical properties of a given material are not the end of the story. Chemical properties are also critical, so let’s take a closer look at them next.

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