2. Components of an insulated transport packaging system

Typically, insulated shipping containers encompass:

Diagram 1

Insulating with Gel Ice Pacs

(a) An external cardboard box. This box presents the product logo, labels and shipping information. It also adds an extra-layer for thermal protection, adds physical strength to the package, and allows palletisation of several packages for transportation and storage.

(b) Thermal insulation. Insulation protects the product against transmission of heat through the walls of the package. Examples of insulation are: combinations of corrugated fibreboard boxes with EPS foam panels, polyurethane foam, vacuum panels and loose fills (e.g. glass, alumina-silica, perlite, silica,aerogel and adiatomaceous earth, which are packed into gaps between the product and the external carboard box). The most popular embodiment of insulation is the humble polystyrene esky.

(c) A cooling (temperature control) agent. Among the most popular are: dry ice, wet ice, or gel packs that are manufactured with paraffin oils, salt hydrides or polyethylene glycol. All these substances act in the same manner: they change from one physical form to another at a certain temperature, absorbing latent heat from their surroundings in the process. This is why these agents are often called phase-change materials, or PCMs. However, some substances are more effective than others as cooling agents.Table 1 below presents a summary of advantages and disadvantages of dry ice, wet ice and gel ice packs.

(d) A temperature monitor. These can range from sophisticated electronic data loggers coupled with RFID to simple labels that change colour when a threshold temperature has been exceeded.

(e) Bubble wrap. Delicate products such as vaccines, flowers, tropical fruits and live seafood need to be kept cold, while avoiding at the same time superficial freezing through direct contact with the cooling agent.

(f) Dessicants. These are normally used to absorb any condensation inside the package, thus avoiding moisture damage to the product’s individual packaging and also any risks of microbial growth inside the package. Some shipping containers will have a radiation shield (e.g. aluminium foil) in the external and internal walls of the container. In well designed packages, this practice is effective in decreasing the amount of heat entering the package. However, the expense of adding the shield may increase the cost of the package considerably.

Gel Ice Pacs

Table 1: Advantages and Disadvantages of various cooling agents
Type of cooling agent
Dry Ice
  • Very potent coolant.
  • Only suitable for frozen products
  • Carbon dioxide gas is hazardous in confined spaces (e.g. coldstores, trucks, air freight)
  • Can lead to “freezer burn” in frozen goods
Wet Ice (including water and ice mixtures)
  • Cheap and available
  • High specific and latent heat
  • Non-toxic and non-flammable
  • Can cause freezing damage in chilled goods if stored in a freezer before use
  • Ice has a lower specific heat than water
  • Water from melted ice can dissolve components of the packaged product
  • Water from melted solutions with salts and mineral is a significant problem in air freight (highly corrosive in the aluminium structure of an aircraft)
  • Avoids the water leakage problem
  • By avoiding convection within the ice pack, gel pacs significantly slow the heat transfer through the packs
  • Similar latent and specific heat as water ice
  • Cost-benefit of many commercial gel packs is low
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