Why temperature matters in transit
Some goods only stay safe or useful within a temperature range. Fresh food, flowers, certain cosmetics, laboratory samples, and some medicines are examples. A parcel on a long journey spends time in vans, sorting centres, warehouses, on airport aprons and in aircraft holds, and temperatures in each can differ widely. The challenge is to keep the contents in their range for the whole journey, including the waiting times that no one planned.
The term cold chain describes the unbroken series of storage and transport steps that keep a product at a controlled temperature from origin to destination. A break at any point can spoil the goods, and the damage is often invisible until the parcel is opened. Pharmaceutical and food products are generally subject to detailed rules in many countries, so a business shipping them should check the regulations and its carrier’s requirements before anything else. This article covers the general principles, not the regulatory detail.
Two approaches: passive and active
Passive packaging
Passive systems use insulation and a coolant, with no power supply. A typical pack has:
- an outer carton;
- an insulated liner, commonly made from expanded polystyrene, polyurethane foam or vacuum-insulated panels;
- one or more coolant elements, such as gel packs, phase-change materials or dry ice;
- the product, often in a sealed inner container, with void fill to stop movement.
The design is meant to hold the interior within a range for a set number of hours. The key point is that the time rating is not a guarantee. A pack tested to hold a range for 48 hours under certain conditions may perform differently in very hot or very cold weather, or if it is opened or crushed.
The choice of coolant depends on the target temperature.
- Chilled products often use gel packs or phase-change materials conditioned to a given temperature.
- Frozen products may use dry ice, which is solid carbon dioxide, or deep-frozen gel packs.
- Ambient-controlled products that must avoid heat and cold may use phase-change materials that hold a temperature near room level.
Dry ice is itself a regulated dangerous good in air transport, because the gas it releases can build up in an enclosed space. It is subject to quantity limits, marking requirements and carrier approval. Packaging must also allow the gas to escape, so a sealed airtight container is not suitable for dry ice.
Active systems
Active containers use a powered refrigeration or heating unit to maintain a set temperature. These are typically used for large or high-value consignments rather than ordinary parcels. They depend on a power supply and on trained handling, and carriers may need to approve them in advance.
Monitoring
Knowing that the goods stayed in range is as important as keeping them there. Monitoring options include:
- Single-use indicators, which change colour or display a signal if a threshold has been crossed.
- Data loggers, which record temperature at set intervals and allow a report to be downloaded on arrival.
- Connected sensors, which transmit readings during transit, allowing a response before the goods spoil. These are a form of IoT sensors.
Monitoring results can support a claim and help decide whether goods should be used or discarded. They also allow the shipper to see where problems occur and to improve the packaging or the route.
Planning the journey
Packaging alone does not make a good cold chain. Most failures come from time and handling rather than from the pack itself.
- Match pack duration to the service. Allow more hours than the expected transit. A delay of a day is common enough to plan for, particularly with weather delays, customs inspection or a missed connection.
- Choose fast, direct services. Fewer transfers mean fewer opportunities for goods to wait on a hot apron or in an unheated warehouse.
- Avoid weekends and holidays. Shipping late in the week can leave goods in a depot for two days.
- Pre-condition the pack and the product. Coolants and insulated liners should be conditioned to the correct temperature before packing, following the supplier’s instructions.
- Confirm acceptance. Not every carrier or service takes perishable or temperature-sensitive goods, and some limit them to certain days.
- Prepare the consignee. Make sure someone can receive the parcel and put the goods into appropriate storage quickly.
- Mark the parcel clearly. Labels such as “perishable” or “keep refrigerated” help handlers, though they do not guarantee special treatment.
For international shipments, import clearance can be a major risk. Inspection of food, plants or biological goods can take time, so documents should be complete and accurate, and customs delays should be considered in the design of the pack. Rules on importing food and biological items vary a great deal between countries, and some goods cannot be imported at all.
Costs and trade-offs
Temperature-controlled shipping costs more. Insulated packaging adds weight and volume, which raises the chargeable weight under the pricing rules in the air freight rates article. Coolants add weight too. Faster services cost more, and monitoring devices add a per-shipment charge. The question is whether the value of the goods and the risk of spoilage justify the cost. Sometimes a cheaper approach is to ship only on days when delivery is more certain, or to use a regional supplier closer to the customer.
When to get specialist help
Standard parcel services have limits. For medicines, medical samples, or high-value perishables, specialist cold-chain carriers and forwarders offer validated packaging, controlled warehouses and documentation. Their services are designed for the regulated side of the business, and a general-purpose courier may not be the right option. If your products are covered by health or food regulations, seek advice from your carrier and the relevant authority before shipping, and test your packaging on a real route before relying on it.