Keeping cool in transit: how goods survive the heat
The bank holiday weekend is bringing the warmest weather of the year so far, with temperatures forecast to reach 30°C in parts of the UK. If that happens before Monday, it will be the earliest the country has hit that mark in over 70 years.
Good news for gardens and barbecues. Less straightforwardly good news for supply chains.
Because while we are all quietly hoping for another hour in the sunshine, somewhere out there a steel shipping container is sitting on a port terminal in direct sun, and it is not having a pleasant time.
The container problem nobody talks about
A standard dry freight container is essentially a steel box. Steel conducts heat extremely efficiently, which means that on a hot day (even a UK-level hot day) the temperature inside an unrefrigerated container can be significantly higher than the air outside it. On a day of 30°C ambient heat, internal container temperatures can reach 50°C or more. In hotter climates, 57°C has been recorded. That is not a storage environment. That is an oven.
And containers do not only sit in ports. They sit on the back of trucks in traffic. They wait at customs. They get stacked in yards. Every one of those moments is another opportunity for heat to build up.
This matters because the list of goods that are genuinely sensitive to heat is much longer than most people assume.
It is not just food and pharmaceuticals
The obvious candidates are well known. Fresh produce, meat, seafood, dairy, vaccines, medications. These have always been shipped under controlled conditions, and the cold chain infrastructure around them is mature and well understood.
But heat-sensitive cargo does not stop there. Here are some that might surprise you.
Electronics. Circuit boards and batteries are vulnerable to sustained heat. The kind of temperature swings a container can experience (cold overnight in port, scorching by midday) can cause condensation inside components, accelerate degradation, and in some cases trigger battery failure.
Wine. Wine exposed to temperatures above around 25°C begins to oxidise prematurely. Above 30°C, the process accelerates noticeably. A container of wine spending a few days in a hot port without temperature control can arrive technically intact but commercially compromised.
Chocolate and confectionery. Chocolate begins to melt at roughly 30–32°C, and once melted and resolidified it loses its temper: the precise crystalline structure that gives it its snap and gloss. A shipment of premium chocolate can arrive looking perfectly normal in its packaging and be entirely unsaleable.
Adhesives. Industrial adhesives often have tight temperature tolerances. Exposure to sustained heat can cause them to partially cure, change viscosity, or lose bonding strength before they are ever used.
Cosmetics and beauty products. Many formulations separate, discolour, or change texture when exposed to heat. The product may look fine in the bottle but perform very differently once applied.
Candles. They melt. Obviously.
The point is that plenty of ambient freight (goods with no refrigeration requirement on the label) quietly depends on not getting too hot. The assumption that temperature control is only for food and pharma is one that can be expensive to test.
How goods are actually kept cool
So how does the industry handle this? The answer ranges from the straightforward to the genuinely ingenious.
Reefer containers are the backbone of temperature-controlled ocean and road freight. Short for refrigerated, these are standard shipping containers fitted with integrated cooling units that can maintain temperatures anywhere from -60°C to +30°C with remarkable precision. Modern units can hold a target temperature to within 0.1°C. They run off the ship’s power supply at sea, and connect to shore power or a generator on land. For long-haul cold chain logistics, they are the standard solution.
What is less widely appreciated is how the air management inside a reefer works. Cold air is channelled underneath the cargo through specially designed T-shaped decking, flowing up through the load and circulating continuously. For cargo that respires (fresh fruit and vegetables produce CO2 and ethylene as they age), reefer units can also exchange fresh air at a controlled rate and manage humidity levels. It is a considerably more sophisticated system than simply “making it cold.”
Modified atmosphere (MA) containers go further still for certain perishables. By adjusting the balance of oxygen, CO2, and nitrogen inside the container, the ripening and ageing process of fresh produce can be slowed significantly, extending shelf life on long ocean voyages without additional refrigeration.
Dry ice has long been the go-to for smaller, high-value temperature-sensitive shipments, particularly pharmaceuticals. It sublimates at -78.5°C, leaving no liquid residue, and can maintain ultra-cold conditions in insulated packaging for extended periods. There is, however, a supply challenge emerging. Dry ice is made from CO2, and tightening CO2 availability (partly a by-product of reduced industrial activity) has created genuine supply pressure, with concerns about shortages continuing into 2026.
Phase change materials (PCMs) are increasingly filling the gap. These are substances engineered to absorb and release heat as they transition between solid and liquid states, making them a more controlled, more sustainable alternative to an ice pack. PCMs can be tuned to specific temperature targets, hold that temperature for longer than gel packs, and are reusable. They are becoming increasingly standard in pharmaceutical cold chain packaging and are making inroads into food logistics too.
Insulated packaging and thermal liners handle the last-mile challenge, where the cold chain is at its most vulnerable. Once a reefer container is unplugged and a shipment is broken down for delivery, maintaining temperature becomes a packaging problem. High-performance insulated liners, vacuum panels, and reflective materials can maintain conditions for long enough to bridge that gap.
Real-time monitoring has transformed the ability to manage temperature in transit. IoT sensors embedded in shipments now provide continuous temperature and humidity data, with alerts triggered the moment conditions drift outside acceptable parameters. The value is not just in knowing something went wrong. It is in being able to intervene before it does, or at least in having verified data for insurance and compliance purposes.
The handoff problem
One thing experienced cold chain operators understand that newcomers often do not is that temperature failure rarely happens in a single dramatic event. It happens at handoffs.
The moment between a reefer container being unplugged at a port and being reconnected to shore power elsewhere. The time a pallet sits on a loading dock while paperwork is processed. The last-mile leg in a vehicle without temperature control.
Each of these is a potential break in the chain, and the chain is only as strong as its weakest link. Planning temperature-controlled shipments means mapping every one of those moments in advance, not just booking the right container.
Summer is a reminder, not an exception
UK summers are not the Gulf. But a heatwave pushing ambient temperatures to 30°C, with a heat health alert issued across the Midlands and south-east, is a useful reminder that temperature risk in freight is not just a concern for shipments to or from hot climates. It exists here, now, during the bank holiday weekend, in a container sitting in Felixstowe or on a truck in a Bank Holiday Monday motorway queue.
The businesses that handle this well do not wait for a damaged shipment to think about temperature management. They build it into their planning from the outset: understanding what their goods actually need, mapping the full journey, choosing the right solution for each leg, and making sure the data exists to verify that everything worked as it should.
The good news is that the solutions available today are better than they have ever been. The bad news is that the bank holiday weekend is still not long enough.
At Green Leaves Logistics, temperature management is part of how we think about every shipment. If you want to talk through what your goods actually need in transit and whether your current arrangements cover it, we are happy to have that conversation.