In Temperature-Controlled Shipping, How Long Do Gel Packs Last?
When shipping temperature-sensitive items such as food, pharmaceuticals, and biotech products, ensuring their integrity during transit is of utmost importance. This is where gel packs come in handy. Gel packs are designed to maintain the ideal temperature for these products during shipping.
But the million-dollar question is, how long do gel packs last in shipping?
Typically, gel packs for shipping are made from a non-toxic, water-based gel enclosed in a leak-proof plastic pouch. They work by absorbing and releasing heat, maintaining a constant temperature for an extended period.
How long do gel packs last (i.e., keep stable temperatures)?
This is a difficult question since there are so many factors that can influence this:
The starting temperature of the gel pack
The temperature of the gel pack is important as it directly affects the temperature of the product it protects. The gel pack works by absorbing and releasing heat to maintain a constant temperature, and the temperature of the gel pack determines the rate at which it can absorb and release heat. If the gel pack is too cold, it will not be able to absorb enough heat to maintain the desired temperature of the product, and if it is too warm, it may release too much heat, causing the temperature of the product to rise.
Gel packs do not necessarily “melt” from a solid to a liquid state; they simply absorb and release heat. When the gel pack absorbs heat, it softens, and when it releases heat, it becomes firmer. The temperature of the gel pack will vary depending on the temperature of the environment and the product it protects.
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Ingredients in the gel
The ingredients in a gel pack can significantly affect its temperature melt point, as they determine the thermal properties of the gel pack. The main ingredients in a gel pack include water, a gelling agent, a stabilizer, and sometimes a preservative.
Water is the primary component of a gel pack or PCM, and it plays a crucial role in determining the thermal properties of the gel pack. The amount of water in the gel pack affects its ability to absorb and release heat, affecting its temperature melt point.
The gelling agent, such as sodium polyacrylate, turns the liquid mixture into a gel-like substance. The type of gelling agent used can affect the thermal properties of the gel pack and its temperature melt point.
The stabilizer, such as potassium chloride, helps maintain the gel pack’s consistency over time, prevents it from breaking down, and can also affect the temperature melt point of the gel pack.
Finally, a preservative, such as sodium benzoate, may be added to the gel pack to extend its shelf life and prevent bacterial growth. The type and amount of preservative used can also affect the temperature melt point of the gel pack.
The surrounding environment's temperature
The gel pack works by absorbing and releasing heat to maintain a constant temperature for the product it protects. Suppose the environment temperature is higher than the temperature of the product. In that case, the gel pack will need to absorb more heat to maintain the desired temperature, which will cause it to lose its ability to absorb and release heat more quickly.
Conversely, if the environment temperature is lower than the product’s temperature, the gel pack will emit less heat, extending its lifespan.
In hot environments, the gel pack will work harder to absorb heat, and its temperature will rise, causing it to lose its ability to absorb and release heat more quickly. In this scenario, the gel pack’s lifespan may be significantly reduced, and it may not be able to maintain the desired temperature of the product for the entire duration of the shipment.
In cold environments, the gel pack will easily release heat, and its temperature will remain low. This will allow the gel pack to maintain its thermal properties for longer, extending its lifespan.
A bit about gel pack conditioning (prepping gel packs for maximum stability)
Gel packs must maintain a constant temperature throughout the entire shipping process regardless of external fluctuations. An increase or decrease in temperature of only 2 degrees Celsius can greatly diminish a product’s potency or even spoil it altogether. Accordingly, let’s review the best ways to condition gel packs and provide details on how to get the most out of them.
Gel packs (aka coolants, refrigerants, PCMs, and ice packs) are leak-proof containers designed to maintain the recommended cold chain temperature range inside a cold box or vaccine carrier. Gel packs are used in four ways:
- Frozen solid gel packs are taken directly from the freezer and generally frozen between 20 degrees Celsius and minus-25 degrees Celsius. When added to a passive container, the container’s temperature will drop to well below 0 degrees Celsius and remain there for several hours. Although they stay cold, frozen gel packs should not be used to transport temperature-sensitive products, such as pharmaceuticals, vaccines, or biologics.
- Conditioned gel packs are warmed or thawed at room temperature until melted and start to liquefy. This change usually occurs at around 0 degrees Celsius. If done correctly, this process removes the initial freezing risk without significantly reducing cold life.
- Cool gel packs are kept in a refrigerator and not frozen. This removes the freezing risk but lacks the cooling performance and protection that a frozen gel pack offers.
- Warm gel packs remain at room temperature and are typically used in extremely cold climates to prevent damage to freeze-sensitive vaccines. This article will strictly focus on frozen and conditioned gel packs. After selecting a gel pack type and observing its temperature requirements, it is imperative that you duly freeze it and then condition it to maximize effectiveness.
A properly conditioned gel pack can prevent the product from freezing when in a vaccine carrier. With that noted, you may need your gel pack to be frozen or refrigerated.
Read more about gel pack conditioning on this article “How to properly condition gel packs for pharmaceutical and vaccine shipping.“
The amount of insulation the container offers (ie EPS coolers)
Insulation helps regulate the temperature of the environment surrounding the container, which in turn affects the temperature of the gel pack.
A well-insulated container (such as an EPS cooler) will help keep the environment temperature stable, reducing the gel pack’s workload. As a result, the gel pack will maintain its thermal properties for longer, extending its lifespan. If the environment temperature fluctuates, the gel pack will have to work harder to absorb and release heat, which will cause it to lose its ability to absorb and release heat more quickly.
In addition, insulation helps to reduce heat transfer between the environment and the product inside the container. This reduces the amount of heat the gel pack has to absorb or release, extending its lifespan.
The type of insulation used and the thickness of the insulation also play a role in determining how long a gel pack will last. Materials like polystyrene or polyurethane offer better insulation properties than materials like cardboard. The thicker the insulation, the better it will be able to regulate the temperature of the environment and reduce heat transfer, extending the lifespan of the gel pack.
Starting temperature of the item you are storing or sending
The starting temperature of the item you are storing or sending affects how long a gel pack will last because it determines the amount of heat the gel pack has to absorb or release.
If the starting temperature of the item is higher than the desired temperature, the gel pack will have to absorb heat to bring the temperature down to the desired level. This will cause the gel pack to lose its ability to absorb and release heat more quickly, reducing its lifespan.
On the other hand, if the starting temperature of the item is lower than the desired temperature, the gel pack will have to release heat to bring the temperature up to the desired level. This will reduce the workload on the gel pack, extending its lifespan.
The size of the pack
A larger gel pack has more thermal mass, which means it can absorb and release more heat. As a result, a larger gel pack will have a longer lifespan compared to a smaller gel pack, as it will have a better ability to maintain the desired temperature of the product for a longer period.
However, a larger gel pack also has more surface area, which means it will lose heat more quickly. This will cause the gel pack to lose its thermal properties more quickly, reducing its lifespan.
On the other hand, a smaller gel pack has less thermal mass, which means it will have a lower capacity to absorb and release heat. As a result, a smaller gel pack will have a shorter lifespan than a larger gel pack, as it will have a weaker ability to maintain the desired temperature of the product for a more extended period.
So what is the answer?
As you can see, there is no clear answer to the question because of the number of factors involved. That being said, the answer is…it depends.
Without insulation, a standard gel pack can last from a few hours to a day or two, depending on the ambient temperature and the temperature of the item being stored or shipped. In high temperatures, the gel pack will have to work harder to absorb heat, causing it to lose its thermal properties more quickly, reducing its lifespan.
With proper insulation, a standard gel pack can last anywhere from several days to a week or more, depending on the factors mentioned above. Insulation helps to regulate the temperature of the environment, reducing the workload on the gel pack and extending its lifespan.
How to select the right gel pack for your shipping environment?
Most packaging companies and carriers would tell you that you need to do some testing before shipping anything, especially if temperature sensitivity can be the difference between life and death (ie medication and vaccines) or if the temperature can cause spoilage of the product. Improper temperatures can also cause the product just to appear to look bad (think melted cheese, moldy nuts, or crystalized chocolates).
We recommend you meet with a packaging expert and perhaps do a test run in a lab before committing to your customer deliveries.
Contact TempAid for a gel pack conditioning analysis, packaging study, and consult. Our team of experts will help you determine the right type and size of gel pack for your shipping needs, ensuring that your products arrive at their destination in perfect condition while saving you costs. We have an ISTA-certified thermal lab and access to millions of data points in real-world shipping conditions to build the ideal temperature profile and packaging environment for your needs.