Thank you for viewing. I purchased this new online in November 2024. I only tried it out and have stored it, virtually unused. It is a standard size. Instruction manual included. Please consider it! —————— 【Improved Ventilation】 VENTAPAK creates airflow between the backpack and your body, enhancing comfort. This prevents back sweat even during extended use. 【Posture Improvement】 This system reduces stress on the back and helps maintain proper posture. It is particularly effective when carrying heavy loads. 【Ergonomic Design】 The ergonomic design fits the body easily and provides a comfortable feel. - Brand: VENTAPAK - Product Name: Backpack Ventilation System - Features: Reduces back stress - Functions: Improved ventilation and posture improvement - Material: Mesh - Condition: Unused Heat, sweat, countermeasures