A data cabinet is disclosed, having a cabinet body for enclosing one or more rack-mounted units, the cabinet body having an inlet for allowing a cooling medium to enter the cabinet and an outlet for allowing the cooling medium to exit the cabinet, a rack for supporting the one or more rack-mounted units within the cabinet body, and one or more sealing members. The rack and the cabinet body define a first plenum space in fluid communication with the inlet and a second plenum space in fluid communication with the outlet. The sealing members substantially block the cooling medium from flowing between the first and second plenum spaces, whilst permitting the cooling medium to flow from the first plenum space to the second plenum space through the one or more rack-mounted units. This arrangement can improve the cooling efficiency, by increasing the flow rate through the rack-mounted units.