Energy, Equivalency, Consistency: How Do Your Gel Packs Measure Up?

By Carli Derifield, MS
(Huntington Beach, CA)


Figure 1. Enthalpy per unit of gel varied widely between brands, from 357 J/g to 406 J/g. Two out of six (33%) were found not to be equivalent in their heat content per unit weight of gel within the same batch/lot of the same brand by �5%, highlighted in red circles.
(click image to enlarge)

The Pharma Bio Transport column, “Five Essentials of Gel Refrigerant Design and Specification,” in the June 2008 issue of PMP News emphasized the importance of the relationship of all qualified components to the performance of a solution for safe and compliant transportation of temperature-sensitive products (TSPs).

Most companies, however, do not have the desire to custom-design and manufacture their own gel packs. Instead, they look to readily available gel packs on the market. Answer two key questions when evaluating gel packs for your solution: How much energy* will be released from the gel pack when transitioning from the frozen to the liquid phase? Can that gel pack brand provide consistent and equivalent energy* from pack to pack within the same brand? *Note: energy is commonly used interchangeably with enthalpy or heat content when discussing gel packs.

Component qualification (CQ) is an integral part of any master validation plan (MVP). The sum of the components equals the solution. If you are not qualifying all the components of your solution for repeated equivalent performance, then is your end-solution really validated? Gel packs are considered to be the heart or battery of any passive solution for the transportation of TSPs. Their size or shape or whether they retain that shape during phase transitions pales in significance to whether you can rely on them to perform equivalently to the level they performed when you qualified them as part of your CQ and validation.

EnviroCooler conducted a side-by-side study of six of the most commonly used gel pack brands. The objective was to assess variability in the equivalency of enthalpy (heat content) stored/released per unit weight of gel among brands (intragel packs) and the equivalency of enthalpy (heat content) stored/released per unit weight of gel within the same batch/lot of the same brand (intergel packs).

In thermodynamics, the enthalpy or heat content (denoted as H, h, or rarely as χ) is a quotient or description of thermodynamic potential of a system, which can be used to calculate the “useful” work obtainable from a closed thermodynamic system under constant pressure and entropy.

During this study, all six brands of gel packs were preconditioned and tested using the same methodology. Gel packs made with distilled water only were used as the control to ensure the testing methodology was validated between each test run. See results in Figure 1.

Table I. The study revealed the enthalpy consistencies (and inconsistencies) within certain brands.
(click image to enlarge)

A closer look at the results in Table I shows the range in enthalpy per unit weight per brand of gel pack (intragel pack) and details the results of variability between gel packs within the same brand (intergel pack). Brand 6 performs the best on both counts of amount of enthalpy interbatch/lot; it is also equivalent or better in terms of the amount of enthalpy per unit weight when compared with each of the other brands. Brands 2 and 5 also performed consistently. Brands 1, 3, and 4 results show that not all gel packs from the same brand are equivalent in their heat content per unit weight intergel pack; as such, they cannot be relied upon for repeated and consistent performance.

The internal environment of a proven passive solution requires a delicate balance of the sum of its components. If your gel packs vary in the amount of heat content, for instance by –10%, a lot of heat content is missing during shipment. If the gel packs you use have 10% more heat content than those with which you qualified your solution, however, more heat content adds to your solution during shipment.

Ask yourself if there is enough, but not too much, energy to bring your solution into thermal equilibrium within the required temperature range quick enough. See if there’s enough, but not too much, to keep it at that required temperature range for the duration required. With too much energy, your product could get too cold; with too little, your product may not get cold enough and withstand the distance.

After investing the significant resources required to select, qualify, and implement a temperature-sensitive packaging solution, select a gel pack provider that can provide the proof of enthalpy equivalency (± 5%) gel pack–to–gel pack.

For a comprehensive copy of the study, e-mail


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