Backpack with breathable holed back, shaped and adjustable holed shoulder straps, sliding chest strap with whistle buckle, adjustable hip belt and breathable lumbar flaps in mesh with external pockets. The main compartment is extendible for a bigger capacity thanks by a zip, the capacity can be also reduced by side compressions straps. The backpack is equipped with one frontal pocket with zip closure, one frontal pocket with fast closure, two external bottle pockets, poles holder and pull-out rain cover in the base. Hydration system compatible.