These wheels are used for industrial purposes. You can use them for wheelbarrows and other load carrying equipment. They can be put on heavier racks to make them mobile. They belong on hand trucks as well. Depending on the job you want to perform, the surface you will be transporting over, and the amount of maintenance you feel is acceptable, you can choose pneumatic (filled with air or foam), or flat free (solid polyurethane).
Pneumatic wheels are often used in an industrial caster context. They consist of a metal hub, a rubber tire mounted to it, and it is filled with air or foam to an ideal pressure for the load it is transporting.
They can fail due to punctures or debris, and they should be refilled regularly for ideal performance.
Flat-free wheels are made of solid polyurethane (typically) and provide some, but not all of the flexibility you’d see with a pneumatic wheel, so rougher terrain, or softer terrain could be more problematic.
They are low-maintenance wheels, but there is a sacrifice on performance. Ideal for non-commercial users.
Semi-pneumatic wheels look like pneumatic wheels. They have a thick, molded rubber outside, and it is hollow on the inside. The performance is between the flat free and the pneumatic in terms of flexibility, and they last longer than pneumatic wheels.