The back is mesh, allowing for cool climbing even under high loads. I used it twice for day hikes. In my subjective opinion, it's in overall good condition. Lowe alpine AirZone Active 18 Product number: FTF-19 Color: Black Size: 52 x 27 x 21cm Weight: 0.77kg Capacity: 18L Back length: 46cm ・AirZoneLT™ system ・With rain cover First come, first served, feel free to purchase immediately. I will ship as soon as possible. Size...11-25 L