Full definition
The maximum percentage increase in gauge length that an elastomer tensile specimen can sustain before breaking, measured per ASTM D412 (dumbbell or ring specimens, 500 mm/min pull rate) or ISO 37. It is a direct indicator of compound flexibility, elasticity, and extensibility. Typical values: natural rubber NR 600-900% (highest of common rubbers), SBR 300-600%, EPDM 300-600%, nitrile NBR 200-600%, neoprene CR 200-600%, silicone VMQ 200-800%, fluoroelastomer FKM 150-300%, polyurethane PU 300-700%. High elongation is desirable for seals (conforming to surface irregularities), flexible membranes, and elastic bands; lower elongation may be acceptable for rigid mounting pads and structural bearings. Elongation decreases with: higher hardness (more filler), higher cross-link density, aging (oxidation breaks chains), and elevated temperature exposure over time. Aging tests (ASTM D573) report elongation retention as a percentage of original — <50% retention indicates significant degradation. Per ASTM D412 and ISO 37. Test temperature: 23 ± 2°C standard.