Sea freight for perishables moves in a refrigerated container, a steel box with its own compressor unit built into one end, plugged into power on the vessel and set to hold a target temperature for the length of the voyage. Air freight moves the same cargo in a temperature-controlled hold or an active container loaded onto a passenger or freighter aircraft, covering the same distance in a fraction of the time at a much higher cost per kilogram. Both keep product cold in transit. They differ enormously in how long that transit takes and what it costs to buy that speed.
The decision is not really about which mode handles cold better. Both hold temperature well when the equipment works. It is about how much shelf life the product has left when it leaves the origin, and whether that is enough to survive a multi-week sea voyage, or whether only a one or two day air transit will do. Freight forwarders and importers make this call per shipment, weighing the same shelf-life clock every time a booking is made, not once per contract.
Shelf life is the gate
A product with weeks of remaining shelf life, most bulk fruit, vegetables and some proteins, can absorb a sea transit of several weeks port to port plus the days needed for pre-carriage and customs on both ends, and still reach the shelf with useful life left. A product with days rather than weeks left, fresh-cut produce, some seafood, cut flowers, anything harvested close to its peak, cannot survive that transit time at all. Air freight's day-or-two transit is the only way the shelf-life math works out. A buyer who miscalculates that clock in either direction pays for it directly: too slow and the product arrives spoiled, too fast and the buyer has paid an air premium a slower mode would have covered just as well.
Cost per kilogram
Sea freight is far cheaper per kilogram moved, because a single vessel carries thousands of containers and the fuel and crew cost spreads across all of them. Air cargo carries a fraction of that volume per flight and burns far more fuel per kilogram moved, so the freight cost alone can run many times higher for the same weight. That gap is exactly what shelf life buys back: paying the air premium only makes sense when the alternative is losing the product to spoilage before it reaches sea's slower schedule. Retailers and food distributors sourcing high volume, low value produce almost always default to sea first and only pay for air when the shelf-life math forces the switch.
Controlled atmosphere on sea
Sea reefer containers can run controlled atmosphere: lowering the oxygen level and raising carbon dioxide inside the sealed box to slow a fruit or vegetable's own respiration, extending its usable life well past what refrigeration alone would allow. That is a lever air freight does not have. An aircraft hold or active air container manages temperature and sometimes humidity, but not the sealed gas atmosphere a shipping line can hold for a multi-week voyage. Controlled atmosphere is part of why some produce that looks too perishable for a sea transit on paper still moves by reefer container in practice. Fruit exporters shipping bananas, apples or other produce with a long dormant season lean on controlled atmosphere specifically to reach markets a straight refrigerated transit could never serve.
Risk concentration
A single reefer container can carry a large, single-lane consignment, so one refrigeration unit failure, one power loss at a transshipment port, or one extended customs hold puts a large volume of product at risk at once. Air freight spreads the same total volume across more, smaller shipments and more frequent departures, so a single failure touches less product. Monitoring the transit in real time on either mode is what catches a developing problem before the whole load is lost, rather than after. A shipper moving a single large reefer booking is effectively betting the whole consignment on one refrigeration unit and one route, in a way that splitting the same volume across several smaller air shipments never does.
Choosing the mode for the product
There is no universally cheaper or better mode, only a shelf-life clock that decides which one still works. Long shelf life, high volume and a cost-sensitive buyer point toward sea. Short shelf life, high value per kilogram and a customer who will not accept a slow transit point toward air cargo. Most sourcing decisions come down to running that shelf-life math honestly for the specific product and route, not defaulting to whichever mode the last shipment used. Neither mode is obsolete for perishables; both keep their own lane.