This Realtree Max4 HD Lens Cover for the Sigma 120-400mm DG OS from LensCoat is a 100% closed-cell neoprene coat that protects the lens from bumps and scratches. It is ideal for nature and outdoor photographers, sports shooters, and photojournalists. It also provides a thermal barrier, protecting your hands from cold lenses in lower temperatures. The cover is waterproof to provide protection in wet weather. It has an optional section that installs via hook-and-loop attachment to cover the lens when it is zoomed to 400mm. The cover can help preserve the resale value of your lens by protecting it from dust, dirt, and other contaminants.