Harkessa wrote a review of The North Face Inferno Sleeping Bag: -40 Degree Down on December 8, 2013
Familiarity: I've used it once or twice and have initial impressions
Great bag - thin cut. If your over 6ft go for the extra length. One flaw is the zipper - it leaks cold air and the inner bevels don't prevent the leakage hitch at minus 40 can be very dangerous. Last addition that north face missed was the silk and mesh breath screen to stop your nose being totally exposed.