I was just getting ready to get the Osprey Atmos 65 backpack for my Appalachian Trail thru-hike. Osprey and REI say a large is 3 lbs. 10 oz. Your review of the 2015 Atmos 65 said a medium would be 4 lbs. 6 oz. Really? Why the significant extra weight?
…It’s a good thru-hiker pack, though I’d also suggest you take a good look at the Osprey Exos 58 for thru-hiking if your gear is light and compact. I used the Exos 58 on a four-day, 86-mile backpacking trip in Yosemite, carrying up to 25 pounds, and on a weeklong hut trek in Italy’s Dolomite Mountains. (My friend, Todd, is carrying the first generation of the Exos 58 on the Pacific Crest Trail at Glen Aulin in Yosemite National Park in the lead photo, above.) I’ve liked that pack a lot since the first version of it came out in 2008.