Temperature-sensitive cargo in air freight faces its greatest thermal risk not at cruising altitude, but on the ground – during tarmac exposure, loading delays, and ground transfers where radiant heat, pressure changes, and unpredictable hold durations combine to create some of the most demanding conditions in global logistics. Understanding what actually happens to your cargo during an air freight journey is the first step to protecting it properly.
The pharmaceutical cold chain, biologics logistics, and high-value perishable freight industries collectively move billions of dollars of temperature-sensitive product through air freight every year. A significant proportion of the temperature excursions that occur during those journeys happen not at 35,000 feet, but in the hours before and after the flight – on tarmacs, in transfer facilities, and during customs holds. This is where thermal pallet covers do – or fail to do – their most important work.
The Air Freight Temperature Journey: What the Data Shows
To understand what a temperature-sensitive pallet actually experiences during an air freight shipment, it helps to map the full journey rather than focusing on the flight itself.
Wilpak conducted a validated 77-hour pharmaceutical cold chain simulation across one of the most demanding air freight routes in global logistics: Melbourne to Chicago via Hong Kong. The simulation was designed by a leading global logistics company to test performance across both summer and winter conditions within a single journey – the route’s geography and season-crossing nature making it one of the most thermally demanding test cases available.
The requirements were stringent: 15ml vials of liquid medication, palletised, transported by air freight over 77 hours, maintaining a continuous temperature range of 0–30°C throughout.
The results were documented and published. InsulCap® constructed from InsulPlatinum® material maintained the internal product temperature between 7.0°C and 24.5°C across the full 77-hour simulation – including periods of exposure to a maximum environment temperature of 34.5°C for five hours, and a minimum environment temperature of -7°C for four hours. InsulGold® maintained internal temperatures between 5.0°C and 27.5°C under the same conditions.
Both results were well within the required 0–30°C range throughout. Neither configuration allowed a temperature excursion.
This is not a laboratory exercise. It is documented evidence of what a validated thermal pallet cover can achieve under the conditions that air freight actually produces – and it is the standard against which any thermal blanket cargo claim for air freight applications should be measured.
Phase 1: Tarmac Exposure – The Highest-Risk Window
The tarmac phase – from the moment a pallet is moved from a temperature-controlled facility onto an airport apron, through loading, and until the aircraft cargo door closes – is the period of greatest thermal risk in air freight logistics.
On a major air freight hub tarmac in summer, a pallet faces:
Direct solar radiation. The sun delivers a continuous radiant heat load to any surface exposed to it. A pallet on a summer tarmac in Hong Kong, Dubai, or Los Angeles is receiving radiant energy from above and from the tarmac surface below simultaneously. The tarmac surface itself can exceed 60°C – well above ambient air temperature – and radiates heat upward into cargo at ground level.
Unpredictable duration. Tarmac holds are not scheduled. A 30-minute planned loading window can become a two-hour delay. A connecting transfer can be extended by a gate change, a crew rotation, or a weight-and-balance recalculation. The thermal protection strategy for air freight cargo must be built around worst-case tarmac exposure, not planned tarmac exposure.
Limited active intervention. Once a pallet is on the tarmac, there is no active temperature control. The thermal blanket cargo solution is the only protection the product has. This is why the solar reflectivity of the outer layer – the primary defence against radiant heat – is the most critical specification for air freight thermal blankets.
InsulCap®’s outer layer is manufactured from the most reflective material available in the market, tested to exceed the ASTM E903-1996 standard for solar reflectivity. When the Melbourne to Chicago trial recorded a maximum environment temperature of 34.5°C for a sustained five-hour period – representing extended tarmac exposure – InsulPlatinum® held the internal product temperature to 24.5°C. That is a 10°C differential between what the environment was doing and what the cargo experienced.
Phase 2: The Flight – Pressure, Altitude, and Why Air Gap Construction Matters
The flight phase introduces a thermal challenge that is less understood than tarmac exposure but equally significant for thermal blanket performance: pressure change.
At cruising altitude, the pressure in an aircraft cargo hold is substantially lower than at sea level – typically equivalent to an altitude of 6,000–8,000 feet even in pressurised holds, and potentially lower in unpressurised sections. This pressure drop has a direct effect on thermal blankets that use conventional air gap constructions.
Conventional bubble constructions – air trapped in thin, unsealed chambers – are pressure-sensitive. As external pressure drops, the air inside the bubbles expands against the membrane, and as pressure is restored during descent, the construction compresses. Over multiple pressure cycles, conventional bubble structures fatigue, lose structural integrity, and provide progressively less insulation. The effective air gap – the still air layer that does the insulating work – is reduced or eliminated.
Military-specification air cylinders work differently. They are engineered to a performance standard that specifically accounts for pressure cycling, maintaining structural integrity and insulating function across the altitude changes of commercial air freight. The cylinders in InsulCap® are validated to retain their form and their thermal performance through the full pressure cycle of a long-haul international flight – not just under ambient ground conditions.
This is the performance difference that makes the military specification relevant to air freight logistics. It is not a marketing distinction. It is the reason InsulCap® maintains its insulating performance throughout a flight while conventional thermal blanket constructions degrade during it.
Phase 3: Transit Hubs and Connections – The Overlooked Excursion Window
For multi-leg air freight journeys – which include most international pharmaceutical shipments – the connection phase introduces a third distinct thermal risk window. The Melbourne to Chicago route via Hong Kong involves unloading at Hong Kong, a transit period, reloading onto a connecting flight, and a second tarmac phase at each end.
Each connection point is a potential excursion event: another tarmac exposure, another loading delay, another period without active temperature control. The thermal blanket cargo solution needs to maintain its performance not just through one tarmac phase and one flight, but through the full cumulative thermal load of a multi-leg journey.
The 77-hour Melbourne to Chicago simulation was designed specifically to test this. Seventy-seven hours is not a single flight time – it is the full end-to-end duration of a multi-leg international air freight journey including connection times, transit holds, and both ends of the route. The validation covers the entire journey, not just the flight phases.
Phase 4: Destination Unloading and Final Mile
The final unloading phase reintroduces the same risks as the origin tarmac. The destination airport may be in a different climate from the origin – the Melbourne to Chicago route transitions from southern hemisphere conditions through Hong Kong to a northern hemisphere winter or summer, depending on the time of year. The thermal blanket must have sufficient remaining performance margin at the end of the 77-hour journey to maintain protection through the final unloading and delivery phase.
InsulPlatinum®’s validated temperature profile across the full 77-hour simulation demonstrates exactly this: maintained internal temperatures of 7–24.5°C from departure through connection through arrival – without a single temperature excursion recorded at any point in the journey.
What This Means for Your Air Freight Thermal Protection Strategy
If you currently use a basic pallet blanket or conventional bubble-construction thermal cover for air freight shipments, these are the questions worth asking:
Has your current thermal blanket been validated under real air freight conditions?
Not laboratory ambient testing – actual air freight simulation, including tarmac exposure, pressure cycling, and multi-leg transit duration.
Does it have ASTM E903-1996 tested solar reflectivity data?
If your supplier cannot give you a specific solar reflectivity figure from an independent ASTM test, they cannot tell you how their product performs against the dominant thermal threat on an air freight tarmac.
Are the air cylinders in your current thermal blanket pressure-stable?
Ask specifically whether the air gap construction has been tested under altitude pressure conditions. If the answer is no, you are using a thermal blanket that was not designed for the environment you are deploying it in.
Does the validated performance duration cover your worst-case journey time?
Including all connection phases, transit holds, and potential delays – not just the scheduled flight time.
For GDP-regulated pharmaceutical air freight, the answers to these questions are not optional details. They are the difference between a thermal protection strategy that holds up under regulatory scrutiny and one that doesn’t.
Frequently Asked Questions: Air Freight and Thermal Pallet Covers
How do thermal pallet covers perform in air freight?
Thermal pallet covers protect air freight cargo primarily during tarmac exposure – the highest-risk phase of the air freight journey. High solar reflectivity defends against radiant heat from the sun and tarmac surface. Military-specification air cylinders maintain structural integrity and insulating performance through altitude pressure cycling. InsulCap® is the only thermal pallet cover specifically designed and validated for air freight environments.
What happens to cargo temperatures on an airport tarmac?
Tarmac surface temperatures can exceed 60°C in summer at major air freight hubs. The combined radiant heat load from the sun above and the tarmac surface below can drive internal pallet temperatures significantly higher than ambient air temperature if the cargo is unprotected or inadequately protected. Validated testing of InsulCap® showed a maintained internal temperature of 24.5°C during five hours of continuous exposure to a 34.5°C environment.
Does cabin pressure affect thermal blanket performance?
Yes. Conventional bubble constructions experience pressure-driven compression during altitude changes, reducing the effective insulating air gap. Military-specification air cylinders are engineered to retain structural integrity and insulating function under altitude pressure cycling, maintaining consistent thermal performance throughout the flight.
What is the Melbourne to Chicago 77-hour trial?
The Melbourne to Chicago 77-hour trial is a validated pharmaceutical cold chain simulation conducted by a leading global logistics company to test InsulCap® performance across one of the most thermally demanding air freight routes available. The 77-hour duration covers the full end-to-end journey including connection times, transit holds, and both tarmac phases. Both InsulPlatinum® and InsulGold® maintained cargo within the required 0–30°C range throughout, with InsulPlatinum® recording internal temperatures of 7.0–24.5°C and InsulGold® recording 5.0–27.5°C.
How does thermal blanket cargo protection support GDP compliance for air freight?
GDP (Good Distribution Practice) requires documented evidence that pharmaceutical products were maintained within validated temperature ranges throughout the supply chain, including during air freight. A thermal blanket cargo solution with validated performance data – ASTM test results, shipping simulation documentation, and real-world trial results – provides the evidence base that quality assurance teams and regulatory bodies require for GDP documentation.
What is the difference between InsulPlatinum® and InsulGold® for air freight?
Both are configurations of InsulCap® validated for air freight use. InsulPlatinum® uses a double-layer material construction and delivers higher thermal performance margins – recording a maximum internal temperature of 24.5°C during the 77-hour Melbourne to Chicago trial at a maximum environment temperature of 34.5°C. InsulGold® uses a single-layer material construction and recorded a maximum internal temperature of 27.5°C under the same conditions. The right configuration depends on the required temperature range, transit duration, and ambient conditions of your specific route.