Hi, i ordered two bags Aspen Sport this one for me and one - smaller Minesotta 35 for my girlfriend. They have been sent on the same day of the order but we recieved them on the third. Once we recieved them I notieced thatthere is a metal frame in the back of my bag, it is not Chevy, but it is pressing all your staff in the bag. I think indeed it is done so your back can "breath" through the net between this frame and your back, but When We filled the bags we notieced Both did the Minesotta 35 can get more stuff in and its shoulder straps are longer than Milwaukee 40's. I can strongly recommend Minesotta 35, it is big enough to pack my staff for a couple days trip, but in the sametime it is not too big so you look like an Indiana Jones :).