A reefer container is a sea container with an integrated refrigeration unit built into it. The unit runs on electricity, cools the air inside the container and holds the set air temperature. That is the short answer; the real decision questions are how the unit is powered and what job this equipment was designed for.

The unit and the airflow

The unit sits in the container's front wall. It blows the cooled air through floor channels under the cargo; the air rises through the load and returns to the unit along the top. That is why loading a reefer without blocking the air path, and stacking cartons so the floor channels stay open, is a subject of its own.

The set value is an air temperature, not the core temperature of the goods. The unit's log records air as well; goods are measured separately at acceptance. A reefer is not expected to chill warm-loaded goods on the way: the equipment is designed to hold a condition, not to pull one down.

Where does the power come from?

On the ship and in the port the container plugs into a socket; on the road leg a generator set or a power unit on the vehicle takes over. In the hours without power the unit is silent and the reefer is, for that time, only an insulated box. Whose account the plug at the waiting yard goes to is one of the most overlooked lines in contracts.

What a reefer does not solve

The reefer belongs to the port-ship-port lane. It was not designed for store delivery, city rounds or the last mile: it does not fit through doors, it depends on a socket, and its volume is oversized for distribution work. On that layer the cold comes from pre-frozen eutectic plates inside an insulated container; the GEBHARDT Isotec programme is the example of that arrangement. The line-by-line comparison of a reefer and an isothermal container has its own article.

Frequently asked question

How long does a reefer container stay cold when unplugged?

No single number can be given: the time depends on the state of the insulation, the ambient temperature, the fill level and door movements. The plan is built not on trust in unplugged hours but on knowing where and when the next socket will be.