Aside from the 20Ft. and 40Ft. containers, there are a variety of containers, used for special cargo, which cannot be handled with general-purpose containers.
These are referred to as "special equipment."
Shipping with this special equipment cost extra, as their handling is more complex.
Among this special equipment are:
Reefer Containers - For cargo that needs to be cooled
Flat Rack Containers - For cargo which falls outside of the standard container dimensions
Open Top Containers - For cargo that is too high for standard containers
High Cube Container - For cargo that is light, but very voluminous (depicted on the right side, compared to a GP 40ft. container)
Flexi Tanks - For liquid, non-hazardous cargo; basically a plastic container for 20-ft. containers, in which the liquid is stored: