DESC: Features: Lightweight durable Polycarbonate ABS Shell material for strength and provide maximum impact resistant, The Polycarbonate allows the shell to absorb impact by 'flexing' when under heavy stress, The ABS is then added to give the shell greater rigidity so that it will not permanently deform when under pressure but instead 'pop' back up into its original shape, Four multi-direction Spinners Wheels for effortless rolling on the 24" and 28" uprights, 20" Upright wheels are located on the outside edge of the luggage to provide greater stability and control when rolling over rough terrain.