Five Star Expandable Backpack Ergonomic straps distribute the weight of the backpack to make it easy to comfortably carry a heavy load. Expandable - the main compartment of the backpack expands for up to 4" of extra storage space for textbooks, zipper binders and more. Front pocket also expands up to 3", giving you more room for everything from your calculator to your lunch. Side access zipper allows easy side access so you can get items out of your backpack while it is hanging in your locker. Side, exterior pocket is perfect for holding a water bottle.