Pneumatic Casters feature air filled pneumatic wheels. Pneumatic or air filled  casters are designed for low speed, manually moved applications. The  pneumatic wheels provide a cushioned ride, shock absorption and quiet operation. Pneumatic casters are ideally suited for moving fragile or delicate cargo where caster overall height is not critical. Casters with pneumatic wheels are usually the best choice for use outdoors over rough surfaces ( i.e. gravel ) or on grass. The wide footprint on 8" or larger pneumatic wheels provides stability on gravel and does not sink into lawns. These are commonly used in the Entertainment industry, Air-Cargo industry, and many others. 

Flat Free Wheels have no air in the tires, thus eliminating the possibility of the wheels ever going flat.  The wheels are filled with a foam compound. These wheels provide the same traction and wide footprint needed to roll on grass, dirt and other bumpy surfaces. Flat Free Wheels have a higher capacity and higher initial cost than Air Filled Pneumatic Wheels. However, over time, they may prove to cost less because they last longer. People tend to load equipment only to the weight they can move easily.