Dynamic Seals Where repeated motions act upon the seal as in a circumferential, axial or angular direction, a dynamic condition exists. Repeated actions upon the seal, either regularly or periodic, typify this type of seal; i.e. a piston ring seal or shock absorption mechanism. Design Considerations are more complex than static seals, primarily resulting from the changing stress levels. In addition to the static seal considerations, the environment may require: - Abrasion resistance becomes important and is affected by the mating surface finishes. - Recovery speed after compression to the original released height. - Compression set, or the percentage of relaxation of the dimensions versus the original uncompressed dimensions - Temperature changes, thermal cycling. - Distortion: squeeze, stretch - ability to recover. - Physical strength: tensile strength, tear resistance.