The Osprey Men's Atmos 65 AG Backpack is new for 2015 and was tough to get at REI when I purchased it. The fuss was all about their new Anti-Gravity™ ventilated suspension system. After trying on a variety of models, I did feel that the Atmos had something the others lacked. While I don't love everything about the backpack, it does position the load very well and keeps the back of the pack off of your back which keeps you cooler. A continuous panel of lightweight mesh extends from the top of the backpanel to the hipbelt and contours to your body. My typical pack weight is around 35 lbs and 65 liters seems to be the perfect size for a mulit-day trip.