Apidura Backcountry Downtube Pack 1.8LThe Backcountry Downtube Pack is designed for storing items underneath the downtube on bikes without accessory mounts. The downtube bag securely fastens to the downtube and similar diameter tubes to provide a versatile and compressible storage space for spares and long distance essentials. It has enough capacity for a 1L water bottle, allowing it to be used as a bottle holder bag for bikes with limited bottle storage space within the main triangle.