Astm C920 Class 25 Vs Class 50 -

The Class 25 sealant stretched well—until it didn’t. At roughly 35% elongation, a tiny hairline crack appeared at the bond line. The Class 50, meanwhile, stretched like warm taffy to nearly double its width, then snapped back without a mark.

The "Class" designation in ASTM C920 refers to the expressed as a number. astm c920 class 25 vs class 50