From AZ Rock: Dyneema is by nature extemely strong, lightweight, yet slippery and these properties make it a great choice to carry in canyon. Longer lengths such as the 8' are great for rescue situations that require improvised mechanical advantage system, while the shorter 4' lengths make a good all around workhorse used from rescue to simply hanging packs on rappel.
Manufacturer Info: An essential part of any alpine climber's rack, Black Diamond Dynex Runners are indispensable for building anchors, slinging natural features or extending placements to reduce rope drag. This highly abrasion-resistant, lightweight material won't weigh you down and absorbs less water than nylon, making it perfect for big routes and snowy or icy terrain. Each size is also color-coded for quick and easy identification on your harness.