I replaced my nylon slings with Dynex ones, but I read that nylon can be preferable because nylon slings stretch under load and help absorb impact on the protection system. Is this true?
Just because the mob repeats something doesn’t make it true. Sling stretch is inconsequential. It doesn’t matter whether that sling is made of stretchy nylon or nearly static material such as Dynex or Dyneema. Stretching is the rope’s job. A lead rope in a CE-type fall might stretch 30 percent, or 69 feet for a 70-meter rope. A 48-inch nylon sling stretching 30 percent would only yield 14 inches, and you won’t get nearly that because slings aren’t made to stretch. As you can see, it’s a simple case of a lot versus a little. Stretch can be a factor for a cordalette and its offspring, the things you use to equalize anchors. Under a high load a nylon cordalette will stretch (a bit) and help (a bit) to equalize the load across the anchors. Yet that attribute is less important than you may think because every anchor piece should be bomber—if you are counting on stretch to save the day, start contemplating your witty last words now. Nylon cord and slings can make some difference when the climbing rope isn’t in the system, as when you clip yourself directly to the anchor with a sling. In this scenario if you were to stupidly move about and fall with slack in the sling, you would shock load the anchor and yourself, and the stretchier nylon will slightly soften the jolt, leaving you with only one ruptured organ. Gear Guy has spoken!