this little backpack from REI is a workhorse. I have stuffed the main compartment with enough gear for warm weather overnighter. It also features a stuffit pouch, pouch for up to 3L hydration bladder, a front zip pocket, two mesh water bottle holders, and a top zip brain area to store easy access items. the back padding has air channels to help. keep you cool, there is also an accessory loop on both shoulder straps as well as a chest strap and hip padding to help carry the load. It also hast a gear loop in case you want to hang an ice ax or some other piece of equipment from it. The pack is in great shape without any holes and has been a solid performer. I don't know the exact volume on this one but I would guess it's about 25 L. The size is medium and should fit most people unless you're over 6 ft.