The humble sling gets less attention than quickdraws, but it is an essential piece of gear. Slings reduce rope drag, can be cinched around trees or thread icicles or equalize anchors. Also, unlike quickdraws, a sling can provide a rappel point anchor where there are no chains or rings.
Sewn slings are made of a few main types of materials. Nylon, and more recently, polyester webbing, are affordable and strong. Polyester has the advantage of not being weakened when wet or absorbing water, unlike nylon. These are obvious advantages for multi-pitch, alpine, ice and mixed climbers.
The Petzl Anneau is a great example. It comes in 60 cm, 80 cm, 120 cm, and 150 cm. These are sewn in the traditional loop format that can be carried around your neck and under your arm in the longer lengths, or racked up doubled.
The other main type of sling material is ultra-high-molecular-weight (UHMW) polyethylenes, which are in Dyneema, Dynex and Spectra webbing. The main advantages of these slings are that they are light and compact for their strength and UV resistance.
They are a popular option, therefore, with alpinists, big wall climbers and anyone climbing where weight and bulk are serious considerations. A new model is the Black Diamond Rabbit Runner.
This 110 cm sling is made of 13mm Dynex and weighs just 35 grams. To reduce weight even further, the sling is a single strand with a larger loop on one end and a tighter carabiner hole on the other.
This allows the sling to be hitched around trees or icicles, or used as a runner. Both of these slings are tested to 22kN.