Here are inflatable and are a pain in the butt to inflate. the stems are to short I must remove the tires to service. Amazon does sell that size tire solid rubber, If the wheels were slit hubs I would get them but I haven't figured out how to get the solids on the wheel with no tire tools.
The tires are solid Polyurethane PU Foam covered in plastic. The foam mimics air tires. It is covered in Plastic to give it a strong outer shell. You never need to inflate them.