Gel packs, also known as cold packs or ice packs, are used in cold chain shipping to help maintain refrigerated temperatures for temperature-sensitive goods while in transit.
The types of temperature-sensitive goods that gel packs can help protect include pharmaceuticals, medical samples, meats, dairy products, beverages, pastries, fruits and vegetables.
However, as a supplier or distributor of such goods, you must consider some key factors to determine how much refrigerant should be used to maintain the desired temperature range for the full length of the shipping duration.
In this guide, we’ll discuss exactly how gel packs work and the various factors at play that determine their effectiveness. While there is no exact formula for calculating how many gel packs to use, this will give you a good idea of your needs.
How do gel packs work?
Refrigerant gel packs are made using a gel solution that is frozen prior to shipment, and slowly thaw when subjected to temperatures above 1 °C. As they thaw, they absorb heat from the ambient air outside the package that may have penetrated to the inside, helping to maintain cooler temperatures inside the package. Once the gel packs have completely thawed to a liquid state, they no longer refrigerate the shipment.
The higher the temperature that the gel packs are exposed to, the faster they will thaw. This means that a larger quantity of gel packs would be required to refrigerate shipments that are exposed to higher temperatures.
Which factors impact the number of gel packs required?
The number of gel packs that are required to maintain the desired temperature range for your shipment depends on various environmental factors. These include:
1. Insulated packaging type and performance
The quality of the insulated packaging being used directly affects the quantity of gel packs required to maintain the desired temperature range throughout the shipping duration.
High-performance insulated packaging, such as our PopupLiner material, features advanced technology that substantially reduces heat transfer. When using this type of high-performance insulation, less heat enters the package, and the gel packs inside the package are therefore subjected to lower temperatures and thaw at a slower rate. This means that a smaller number of gel packs can effectively refrigerate the shipment for a longer duration.
Insulated packaging that is less effective, on the other hand, allows more ambient heat to enter inside the shipment. This results in gel packs thawing at a faster rate, and a larger quantity of gel packs are consequently required to insulate the shipment
2. Ambient temperature
The ambient temperature that a shipment is subjected to also has a significant bearing on the number of gel packs that are required.
If a package is subjected to extremely high ambient temperatures during shipment, more heat will enter the package, and a larger quantity of gel packs will be required to maintain a cool payload temperature.
If ambient temperatures are less extreme, on the other hand, gel packs inside the shipment will thaw more slowly, meaning fewer will be required to provide sufficient refrigeration throughout the transit duration.
3. Shipping duration
Since gel packs thaw over time and lose their ability to absorb heat once they reach a liquid state, the shipping duration is a crucial factor in determining how many gel packs are required.
For shorter shipments (such as those of 24 hours or less), fewer gel packs are needed as they are likely to remain frozen throughout the shipping duration. For longer shipments (such as those from 48 to 96 hours), a larger quantity of gel packs will be required, wherein a prolonged thawing will keep the products cool throughout the shipping duration.
4. Payload size and target temperature
The number of gel packs you need is directly related to the size of your payload and its target temperature range. Products that need to be kept colder, such as refrigerated meats, will need more gel packs than products that can be safely stored at controlled room temperature.
The number of gel packs required also increases based on the volume of products being shipped. A package containing a larger volume of products will require more gel packs than a smaller package.
As a general rule of thumb, for food and other dairy products it is recommended to use one pound of gel packs for every cubic foot of product with a target temperature of below 41 °F over a 24-hour period. The accuracy of this, however, will depend on ambient temperatures and the type of insulation used in the packaging.
The payload pre-shipment temperature is another key factor to consider. The temperature differential between the ice packs and the payload can affect the duration of thawing as well as condensation inside the package.
Placement of your gel packs is another important factor to consider
Finally, how gel packs are placed inside the package is critical.
Maintaining a good fit will ensure that first, the gel packs do not over-chill products that can’t get too cold. Flowers, herbs and other produce cannot get too cold or they will be damaged, so they should be placed farther away or have a buffer between them and the ice pack. However, other items where cold temperatures are critical like meat, fish, chicken and other proteins can be placed close to or touching the ice pack.
During the shipment, gel packs soften as they thaw. This can cause movement or shifting inside the package and can therefore affect the performance that depends on the positioning of the ice pack. To prevent shifting, inserts and other dunnage can be used in the design of the pack-out.
Discuss your gel pack needs with IPC
Given the various factors at play, it is difficult to say precisely how many gel packs your shipments will require.
The best approach is to get in touch with us at IPC to speak with one of our experts and discuss your needs.
We can offer tailored solutions to your cold shipping requirements. All of our gel packs are available in custom sizes, meaning they can be perfectly adapted to the dimensions of your temperature-sensitive products and insulated packaging for maximum thermal efficiency.