The Science Behind Ice Packs for Shipping and Their Importance

Ice packs are the backbone of insulated shipping. They are used to keep perishables in frozen or refrigerated temperature ranges (and out of the danger zone) for their entire journey.

These shipments must stay calm to avoid spoilage, whether pharmaceutical drugs or biological samples. So, how do ice packs accomplish this feat?

Endothermic/Exothermic Reactions

When shipped properly, ice packs can remain cold for several days. They’re made with non-toxic, food-safe gel refrigerants and are leakproof, reusable, and odorless. They’re also a safer alternative to dry ice for products that cannot be exposed to frigid temperatures, such as flowers, herbs, and produce.

As the solute dissolves in solution, it releases heat energy into the surrounding environment. The amount of heat energy released varies depending on the temperature at which the solute dissolves in solution. According to Le Chatelier’s Principle, increasing the temperature increases the solute’s solubility, while decreasing the temperature decreases it.

Most ice pack manufacturers use an exothermic salt hydrate, typically ammonium nitrate mixed with water, as the refrigerant in their cold packs. This product is generally marketed as an instant cold or hot product for medical therapy applications. It contains a freezing point depressant (to prevent it from freezing to hard ice in reuse) and a gelling agent to produce a reusable ice pack. These eco friendly ice packs for shipping products are commonly used in cold chain logistics for fresh seafood, pharmaceuticals and health care, pathology, biotechnology, scientific laboratories, confectionary, and air freight shipping. They can also be used with dry ice to slow the sublimation rate and extend its shelf-life. They’re an essential part of the cold chain and crucial for home delivery of perishables such as meal kits, groceries, and pharmaceuticals.

Temperature Reduction

For perishables that need to stay frozen or below a specific temperature, like meats and pharmaceuticals, gel ice packs are the way to go. Thousands of companies use them to keep products within their frozen or refrigerated temperature ranges and out of the danger zone until they’re delivered and opened.

The temperature reduction that comes from a gel pack is far more significant than conventional ice, even when both are packed in an insulated cooler. This is because gel packs have a lower surface area than conventional ice and thus can retain colder temperatures for longer. The exact amount of time a gel pack can remain frozen depends on the size and shape of the package/cooler and its initial temperature.

However, the most critical factor in determining how long a gel pack can remain frozen is the temperature of its payload. The ice must provide sufficient cooling for its payload and not over-chill it. The payload’s pre-shipment temperature also affects the duration of thawing, which is why it’s so critical that our customers follow the proper packing guidelines to ensure maximum product safety and security during transport.

Another significant benefit of gel ice packs is that they don’t evaporate as rapidly as dry ice. This is particularly beneficial when shipping by air, as it eliminates the need to adhere to dry ice safety and packaging regulations and avoids potential delays at airports.

Temperature Regulation

There is no one-size-fits-all solution for temperature-controlled packaging – every product has its own unique set of requirements. This includes the product’s dimensions, the temperature range it needs to stay in, and the time the shipment will be in transit.

For example, ice packs are often used to keep pharmaceuticals and frozen foods cold during shipment. But they are also famous for keeping home-delivered meal kits and fresh food from overheating during transit or helping to keep reagents in laboratories at the right temperature until researchers can open them.

The materials that make up a gel pack are essential to maintain their designated temperature range. The exact composition can vary depending on the manufacturer. Still, most ice packs use a mixture of propylene glycol (an antifreeze chemical), water, dye, hydroxyethyl cellulose, and vinyl-coated silica gel to create a thick liquid that’s both cold and flexible.

This mixture is then poured into pouches that are vacuum sealed with commercial-grade equipment. The packaging is stamped with usage instructions and expiration dates before being sealed in a plastic bag or box and ready for the customer. Unlike dry ice, which turns into CO2 gas during sublimation and is therefore considered a hazardous substance that requires special labeling, handling, storage, and shipping regulations, gel ice packs are completely safe to ship by air or sea.

Moisture Reduction

While some products need to be kept free of moisture for safety or quality reasons, many can benefit from moderate levels of moisture being maintained over a more extended period. This is why it’s so important for manufacturers and shippers to understand the appropriate range of moisture for their products or package to design their shipping methods accordingly.

Dry ice and cold packs are both used to keep temperature-sensitive shipments cool. However, cold packs are more convenient and flexible than dry ice because they don’t require an airtight container or extra protective measures. Plus, they don’t release carbon dioxide during sublimation, potentially damaging the package.

Most reusable cold packs contain a combination of materials that keep them cold, such as a freezable silica gel, hydroxyethyl cellulose, or polymer with preservatives. They also have a small amount of liquid, typically distilled water or sodium polyacrylate, which forms a gelatinous material when it freezes.

Some ice pack materials, like those made of cellulose, are even compostable and safe for use in garden soil. They’re also safer than other ice pack options that can cause chemical burns when mishandled. For example, an ice pack stored in a Styrofoam box for too long can start to leak and cause damage. Many of these leaking ice packs end up in general waste bins, but you can avoid this with Tempack’s pre-qualified cooling solutions.