The "fill power,' a measurement of the down's density, is 700 cubic inches per ounce, higher than most mummy sleeping bags. The shell is not just Gore-Tex, but an even more outdoorsy composite L.L. Bean calls Rugged Gore. The Windstopper is advertised as comfortable to 40 below zero. This jacket is in nice condition with no known flaws and only a couple small marks from normal signs of wear as can be seen in the pictures. Please ask any questions you think you may have to ensure a confident purchase.