The wheels of trolley suitcases, also known as rollers, are made out of polyurethane, rubber or plastic. Polyurethane wheels, made of a flexible, durable type of plastic, stand up best under use. Regular plastic or rubber wheels either wear down too quickly or move too slowly in comparison. Spinner suitcases, in which the wheels rotate 360 degrees, ease the strain of travel for many.
In roller suitcases, the wheels are recessed into the case, which protects them from snapping off during rough handling. Wheels that are recessed allow more space in the interior packing area of the airplane's cargo area. If the suitcase is just being used to travel on sidewalks, two-wheelers are better than four-wheelers for clearing curbs and rolling on uneven surfaces. However, the dragging motion involved with in-line wheels bothers some people's shoulders, wrists and backs. Dragging a roller suitcase into a crowded area is more difficult than pushing a spinner, which can stand upright. Spinner suitcases are easier to manage and navigate in tight spaces. However, the wheels can break off more easily because they aren't protected. In addition, spinners do not stay still on an incline, and they take up more room in the cargo area.