Thank you for viewing. I purchased this new online in November 2024. I only tried it out and have stored it, so it's practically unused. Standard size. Instruction manual included. Please consider purchasing! —————— 【Improved Ventilation】 VENTAPAK creates airflow between the backpack and your body, improving comfort. This prevents back sweat even during extended use. 【Posture Improvement】 This system reduces stress on the back and helps maintain correct posture. It's especially effective when carrying heavy loads. 【Ergonomic Design】 Ergonomically designed to fit the body easily and provide a comfortable feel. - Brand: VENTAPAK - Product Name: Backpack Ventilation System - Features: Reduces back stress - Functions: Improves ventilation and posture - Material: Mesh - Condition: Unused Heat, sweat, countermeasures