This union 34 stripe rucksack is a 30 litre capacity bike backpack with a hidden plastic fitting in its back which enables it to slot securely to the seatpost fixing system and stay there ndash even over rough or bumpy terrain off the bike this urban rucksack not only looks professional and compact but can be carried in comfort thanks to the ample padding around the shoulders and back and the airflow around the spine for maximum support and comfort inside there are dedicated spaces