This is a Butler Creek Sling known as the Comfort Stretch, model 80023.
Its stretchable construction and soft padding soak up the bounce you get with traditional slings - reducing felt weight up to 50% - so even the roughest hikes are smooth on your shoulder.
Features:
Soft flexible closed cell neoprene with Comfort Stretch backing;Dramatically reduces felt weight;Non-slip Grippersâ„¢ keep it firmly in place