Packaging and compliance
Packing perishables for air freight: what changes from sea
Sea freight packaging and air freight packaging solve different problems. A reefer container holds temperature for three weeks with the vessel's own power, so the pack mainly has to survive handling and stacking. Air freight has none of that: no continuous power on most legs, a bill that scales with volume as much as weight, and a pallet that has to conform to an aircraft's internal shape rather than a container's straight walls. Getting this wrong shows up two ways: an inflated freight bill from an oversized pack, or product that arrives warm because the insulation ran out before the last leg did.
Key facts
- Air freight charges the greater of actual and volumetric weight, calculated from dimensions, so an over-built or badly shaped pack can cost more than the coolant it saves.
- Most air lanes have no continuous refrigeration between the packhouse and the aircraft hold: the pack and its pre-cooling do the work that a reefer container does on the sea leg.
- A pallet has to fit a specific unit load device contour, not just a footprint, and the ULD's own curvature and net rules constrain stack height and corner build in ways a sea container does not.
- Insulation, coolant, and ventilation trade off against each other and against chargeable weight: the right pack for a 6-hour lane is usually wrong for a 30-hour one.
Why volumetric weight decides the pack, not just the product
Air freight is billed on chargeable weight, the greater of actual weight and volumetric weight. Volumetric weight is calculated from the outer dimensions of the shipment, typically length times width times height in centimetres divided by 6,000 for a kilogram figure (some carriers use 5,000 for their own tariffs, so check the specific airline's divisor before quoting a customer). For most perishable packs, which are light relative to their bulk, volumetric weight is the number that actually applies, not the scale weight.
This means every centimetre of insulation, every void filled with polystyrene rather than product, and every corner post or edge protector adds directly to the bill, not just to handling cost. A pack built the way a sea freight team would build it, with generous insulation and loose stacking for safety margin, can quietly turn a 400kg shipment into a 900kg chargeable one.
The practical rule: design to the tightest dimensions that still protect the product and hold temperature for the transit time, then check the resulting chargeable weight against actual weight. A wide gap between the two means the pack is oversized for what it carries, and that gap is pure cost with no protective benefit.
No continuous cold chain: the pack does the refrigeration
A reefer container has its own compressor and runs at a set point for the whole sea voyage. Air freight rarely offers that. Standard cargo holds are pressurised and heated to protect the aircraft and general cargo, typically held somewhere in the range of 15 to 25 degrees Celsius depending on the aircraft type and loading, not refrigerated to a perishable's target temperature. A small number of wide-body aircraft carry active cool-chain containers (Envirotainer and CSafe are the names to look for), but these are limited in number, cost significantly more to book, and need to be reserved specifically, not assumed as available.
For everything not in an active container, protection comes from three things happening before the aircraft door closes: pre-cooling the product to target temperature before packing rather than relying on the pack to pull heat out afterward, the insulation and coolant holding that temperature through tarmac time, ramp transfer, and any transit stop, and minimising time outside temperature control, particularly on the ramp in direct sun, which is where most excursions actually happen rather than in the air.
A worked example: a berry shipment pre-cooled to 2 degrees Celsius and packed with gel coolant rated for 24 hours holds its target range through an 8-hour direct flight with margin to spare. The same pack on a routing with a transit stop and a total elapsed time of 30 hours from packhouse to destination cold store runs out of coolant capacity partway through, and the product arrives having spent several hours above target range, most of it not in the air but sitting on a ramp or in an unrefrigerated transit warehouse.
Insulation, coolant, and the weight penalty
Every insulation and coolant choice trades thermal performance against volumetric and actual weight, and air freight punishes both sides of that trade harder than sea freight does. Expanded polystyrene is cheap and light but bulky, which hurts on volumetric weight. Vacuum-insulated panels hold temperature far longer per centimetre of thickness but cost more per box and are usually reserved for high-value pharmaceutical-grade or premium fresh produce shipments where the freight premium is worth it. Corrugated board with a reflective liner sits in between: adequate for short transit times, inadequate once total elapsed time passes roughly 24 hours.
Coolant follows the same trade. Gel packs and phase-change material add real weight, usually 15 to 25 percent of product weight for a pack designed to hold temperature through a full day, and that weight counts on both sides of the chargeable weight calculation since coolant occupies volume too. Dry ice cools more efficiently per kilogram but is regulated as dangerous goods on aircraft: IATA's Dangerous Goods Regulations set quantity limits per package and per aircraft, and it must be declared and labelled accordingly, which adds documentation and can restrict which flights and forwarders will carry it.
The decision rule that actually works: size the coolant to the true elapsed time from packhouse to destination cold store, including any known transit stop and ground handling window, not to flight time alone. Flight time is usually the shortest part of the journey; ramp and transit time is where most packs run out of thermal capacity.
Ventilation versus insulation, and why you cannot maximise both
Fresh produce that is still respiring, most fruit and vegetables, needs airflow to carry away the heat and carbon dioxide it generates and to prevent condensation building up inside a sealed pack. A fully sealed insulated box holds temperature well but traps that respiration heat and moisture, which can do more damage over a long transit than a modest temperature rise would.
The two goals pull in opposite directions: more insulation means less airflow, more ventilation means less thermal holding power. The practical resolution most packers use is a vented inner liner or perforated tray that lets air move around individual units, inside an outer insulated shell that controls the overall temperature envelope, rather than either a fully sealed box or an open vented carton with no insulation at all.
Which side of that balance to favour depends on the product and the transit time. A low-respiration item like citrus on a short flight can tolerate more sealing and less ventilation. A high-respiration item like leafy greens or soft berries on a longer routing needs the ventilation prioritised, even at some cost to how long the pack holds its target temperature, because condensation and heat buildup will spoil the product faster than a few degrees of temperature drift.
Building a pallet that actually fits the aircraft
Sea containers are rectangular boxes; the pallet build inside one only has to respect the container's straight walls and a weight limit. Unit load devices are shaped to the curve of the aircraft fuselage, and that curvature is not optional: a pallet or container built taller or wider than the ULD's contour envelope will not clear the aircraft door or the hold, and it gets bumped or rebuilt at the last minute, which is exactly when a perishable shipment cannot afford a delay.
The most common lower-deck ULD for freighter and belly-hold cargo is built to a base roughly 2.24 by 3.18 metres (an LD3 or a pallet built to an LD3-equivalent contour is common for smaller shipments; larger freighter-only loads use bigger pallet positions). Height allowance tapers toward the edges to follow the fuselage curve, so a pack that is a uniform height across its full footprint will not fit unless it is built with that taper in mind, stepping the stack down toward the edges rather than building a flat-topped cube.
Build rules that hold regardless of the specific ULD: keep the load within the net or strap envelope so the ramp handler can secure it without repacking, keep cartons from overhanging the pallet edge since that is what gets a shipment rejected at the ramp, and confirm weight distribution against the ULD's own load limit, usually lower than the aircraft's overall cargo weight limit per position. Confirm the actual contour and weight limit for the specific ULD type your forwarder is booking, since these vary by aircraft type.
Labelling and handling marks that get read
A perishable shipment moves through several handoffs between packhouse and destination: trucking to the airport, airline ramp handling, possibly a transit warehouse, then destination handling and customs. At each handoff, the label is often the only thing that travels with the box that a new handler actually reads before deciding how to treat it, so it has to carry the essential information without requiring anyone to look up a waybill.
What actually gets read: a temperature range stated as a number rather than a generic 'keep cool' instruction, a 'this way up' or fragile mark where the pack genuinely cannot be inverted, and a perishable or time-sensitive marking visually distinct from general cargo markings, since ramp staff handling mixed loads triage by what they see at a glance, not by reading fine print. A label buried among shipping marks, customs codes, and carrier barcodes competes for attention and tends to lose.
The practical habit worth building: put the temperature range and the perishable marking on at least two faces of the pallet or box, not just the top, since a pallet loaded into a ULD often has only its sides visible to the handler moving it. A single top-face label on a stacked or netted load is effectively invisible during the handling steps that matter most.
Two packs compared: chargeable weight and arrival condition
A worked comparison, illustrative rather than a specific real shipment: 200 kilograms of packed stone fruit built two ways for the same 10-hour routing including a transit stop. Pack A uses a deep expanded-polystyrene shell, generous gel coolant sized for 48 hours of holding, and loose stacking for handling safety margin, giving outer dimensions of 120 by 100 by 90 centimetres. Pack B uses a thinner vacuum-insulated liner, coolant sized to the actual 10-hour elapsed time with a modest safety margin rather than a worst-case one, and a build that hugs the ULD's usable envelope, giving outer dimensions of 100 by 80 by 70 centimetres.
On chargeable weight: Pack A's volume works out to roughly 216 kilograms of volumetric weight at a 6,000 divisor, against 200 kilograms actual, so it bills on the higher figure. Pack B's volume comes out to roughly 93 kilograms volumetric, well under actual weight, so it bills on the 200 kilogram actual figure instead. Pack A is paying a volumetric premium for coolant capacity it does not need on a 10-hour lane; Pack B is not.
On arrival condition, both packs would likely hold temperature adequately for this specific 10-hour routing, since Pack B was sized correctly for the actual transit time rather than for a worst case. The risk sits the other way: if this shipment had instead run 30 hours because of a longer transit stop, Pack B's tighter coolant margin could run out before Pack A's oversized one would. The decision is not that one pack is universally better, it is that the pack has to be sized to the routing's real elapsed time, with a margin for a plausible delay, and re-sized when the routing changes rather than reused because it worked on a previous lane.
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