Packages can experience delays when initially surrendered to the distribution system awaiting pick-up, or at numerous points along the way: at customs, freight forwarders, after-hour deliveries, etc. Well intentioned individuals may see "refrigerate upon arrival" labels on the packages and immediately place them into refrigerated storage. At first blush, this may seem a harmless, even helpful practice. But it can result in disaster for temperature sensitive products where no excursions in temperature are allowed beyond their narrow range.

Unraveling the Myth

Temperature controlled packaging design and performance is characterized by regulating the rate of heat transfer throughout the package. This is acheived by taking advantage of the Latent Heat of Fusion of the gel packs - the energy absorbed in the form of heat that results in a cooling of the surroundings. There is a finite amount of energy the gel packs will abosorb as they melt, or release as they freeze. Thermal packaging attempts to control that energy in a way that maintains the desired temperature of the payload within the package.

You need enough 'gas in your tank' to get you to your destination. The performance and longevity of a hermetically sealed insulated package that contains refrigerant designed to maintain its contents within a specific temperature range, is dependent upon 6 inter-related input factors:

1. The type of insulating material used and its resistance to heat flow (R value)
2. The quantity and the phase change temperature of the refrigerant
3. The temperature to which the refrigerant, product and packaging are pre-conditioned
4. The ratio of refrigerant to product size and mass (and to a lesser extent its geometry)
5. The packing configuration
6. The environment to which the package is exposed (ambient temperature)

Heat moves to cold. Fluctuations in ambient temperature, a normal condition in the transportation environment, will affect the rate of heat transfer. The higher the ambient temperature, the faster the rate of heat transfer, which will decrease the longevity of the package at its specified internal temperature range. Conversely, the lower the ambient temperature, the slower the rate of heat transfer.

Since a certain amount of heat is estimated to enter the package under normal conditions, interfering with or inhibiting that process will cause the package to function improperly.

If excessive temperature (either heat or cold) is applied to a package too quickly, or for extended durations, its ability to maintain the internal contents within a specified temperature range may be exceeded, the extent of which is dependent upon the 6 input factors above.

When a package design includes product and refrigerant all pre-conditioned to 2°-8°C, and it is exposed to a refrigerated environment (2°-8°C) then the package and all of its contents will eventually reach temperature equilibrium.

However, when the package requires frozen gel packs to help maintain its contents at 2°-8°C, exposure to refrigerated temperatures will eventually cause the internal contents to fall below 2°C, to the phase change temperature of the frozen gel packs, typically at or near 0°C. This occurs as the heat transfer from externally applied temperatures slows, and the frozen gel packs, striving to maintain their phase change temperature of 0°C, begin to pull the heat from its surrounding internal contents, including any refrigerated gel packs in the package and, most importantly, the product.