Well dynamic rope is a double braid, polyester jacket over a nylon core. The nylon core stretches quite a bit to mitigate shock absorption. Finally, rope companies supplying arborists are now offering dynamic ropes much like a rock climbers life line. Yale Polydyne, Husky II off of Wes Spur, Dynasorb off of Sherrill Tree. In another example, Jamie Goddard of Yale Cordage recently demonstrated on video a drop test using a 220-pound weight tethered first with dynamic (elastic) line and then with static (nonelastic) line. Tensile strength of the dynamic line was 3 tons, while the static line was 10 tons. The dynamic line arrested the weight six times without failure, while the static line snapped on the first drop. A dynamic line 1/3 the strength of a static line stopped a 220 lb weight 6 times, while the 3x stronger static rope could not stop it once. Rock climbers (such as Dan Osman) know what they are doing. Much more so than tree climbers. If any of you doubt that, just watch all of Dan Osman's videos on Youtube. Rock climbing/rope jumping is much more technical than what we do. That's why they use dynamic line for a life line, and say never should a static line be used for fall arrest, BECAUSE IT WILL SNAP. Never, in the history of rock climbing has a dynamic climbing line meant for life support snapped while arresting the fall of a human (and multiple humans). On the other hand, I can go on youtube right now and watch a video of a large diameter static bull rope snapping from being shock loaded with the tip of a branch. Sending the climber flailing on his climbing line as the limb slingshotted him. This is not the Dan Osman thread? He free climbed (without rope), up a rock face, higher than any tree grows and jumped off cliffs taller than any tree (and jumped out of trees too) with only a dynamic line (ultimately) for a life line.