Hot and cold packs make our lives more comfortable by easing our aches and pains and keeping our food cold. But have you ever wondered how they’re made? From instant ice packs to reusable ones, each style is a little different and works a bit differently.
Without further ado, let’s get into how hot and cold packs are made!
Blend the Solution
The gel solution, which is a combination of water, dye, propylene glycol, hydroxyethyl cellulose, and vinyl-coated silica gel, is mixed in a giant mixer. The gel is then left to sit for about 1 hour so the ingredients fully bind together.
Personalize the Ice Packs
The plastic casing of the ice packs are put together and stamped with usage instructions. This is usually done through pad printing, which involves a large stamp of ink getting pressed onto the plastic.
Fill the Packs
After the refrigerant gel is mixed and the packs have been assembled, they are ready to be put together! The gel is injected into the ice packs and sent to the vacuum sealer.
Vacuum Seal the Plastic
The ice packs are vacuum sealed so all excess air is removed from the pack. If there’s too much air inside, the pack can pop when it’s squeezed. This is one of the most important steps of the manufacturing process!
Inspect the Ice Packs
All ice packs are inspected, tested, and squeezed to make sure there aren’t any tears or leakage. Ice packs that don’t pass quality testing are deconstructed and repurposed so the gel can be used in future ice packs.
Packed for Shipment
The ice packs are packed for commercial shipping and are sent to stores and warehouses across the globe. Some are even sent directly to doctor offices and surgery centers!
Are you a visual learner? Watch this video to see how ice packs are made!
You can find ice packs at most grocery stores, convenience shops, or even gas stations. Each store’s version will be a little different, but they usually follow the same manufacturing process! Don’t forget to read the instructions to be sure you are using the pack properly.
What Chemical is in Ice Packs?
Reusable ice packs contain a combination of materials that keep them cold and flexible. The exact material can vary depending on the type of ice pack and the manufacturing methods.
Most ice packs contain some combination of the materials listed below:
- Propylene Glycol: A synthetic liquid material that is absorbent in nature. The colorless material serves as an antifreeze component, keeping the pack flexible at any temperature
- Hydroxyethyl Cellulose: A thickening agent that is commonly used in household products like shampoo or shower gel
- Vinyl-Coated Silica Gel: A binding material that holds the ice pack solution together and keeps the ice pack cold for long periods of time
- Colored Dye: Most colored ice packs contain blue dye, but manufacturers may choose to add in a different color to their ice pack
- Water: This keeps the mixture flexible and cold
Reusable ice packs that have colored beads on the inside are a bit of a different story. The beads are usually made from sodium polyacrylate, a material that can absorb up to 1,000 times its mass in water!
How Reusable Gel Ice Packs Work
Gel ice packs work because the special material used on the inside allows it to stay cold and flexible. The key ingredient that allows the ice pack to remain cold without freezing solid is propylene glycol. Without it, our ice packs wouldn’t stay cool!
When the propylene glycol mixes with the other materials like water, dye, hydroxyethyl cellulose, and vinyl-coated silica gel, it thickens into a colored mixture that is squishy and flexible. This is super important for reusable ice packs because they’re usually used for injuries. If they weren’t flexible, you wouldn’t be able to wrap them around a knee or ankle!
A gel ice pack should be placed in the freezer for at least 1 to 2 hours before being used.
How Instant Ice Packs Work
Instant ice packs work by mixing water with ammonium nitrate. The two solutions are stored in separate parts of the ice pack, with the water contained in a small inner plastic bag. When the bag of water is popped by applying pressure to the ice pack, the ammonium nitrate mixes with it and causes an endothermic reaction. That’s just a fancy way of saying the material gets really cold and freezes to a solid!
The amount of time an instant ice pack stays cold depends on the size and manufacturing process of the pack. On average, you can expect your instant ice pack to last around 5 hours!
How Do Heat Packs Work?
Heat packs work by warming up the heat-retaining material on the inside, which is usually gel or rice. Depending on the heat pack, they can be warmed up in the microwave, by boiling on the stove, or activating a disc inside. The pack will stay warm for at least 20 minutes or so, depending on its insulation.
Electric heat pads, on the other hand, use electricity to warm you up. This style of heating pad stays warm way longer than the microwaveable kind!
Click Heat Packs
Click heat packs work by bending the small aluminum disc inside, which causes a chemical reaction with the surrounding liquid (sodium acetate and water). Once the disc is bent and the reaction starts, the pack will quickly turn from a liquid to a solid. The process of changing to a solid is what makes the pack feel warm to the touch since it generates heat!
To reuse your click heat pack, you’ll need to place it in a pot of boiling water. The heat of the water causes the crystallized ice pack to melt back to its liquid state so you can continue to reuse it! Just be careful removing it from the water after you’re done.
Electric Heating Pads
A maze of wires is inside of an electric heating pad. The wires all connect at the base of the heating pad where the main power cord is located. When the heating pad is turned on, the power from the outlet goes through the cord and into the system of wires inside. That’s what makes the entire pad so warm!
Most electric heating pads on the market today have three heat settings: low, medium, and high. When you adjust the settings on the remote, it changes the amount of energy that goes into the coil wires. The higher the heat setting, the more power goes into your heating pad.
How Long Do Ice Packs Last?
The average ice pack lasts for approximately 1 to 2 hours. The exact amount of time it remains cold depends on the size of the ice pack, the type of refrigerant gel or beads, and the manufacturing process. There are special styles of ice packs that are meant for lasting longer, like the kind you see in a lunch box or in a commercial shipment. However, most ice packs will stay cold for at least an hour!
Do Ice Packs Expire?
Technically, some ice packs do expire. Many have expiration dates on them simply because the plastic casing may break down over time, which could cause holes to form on the pack.
While most ice packs manufactured today are non-toxic, you should still keep an eye on your ice pack just in case. If you look closely, you might see micro-tears in the plastic lining. That’s a sign that it’s time to retire your ice pack and get a new one!
The Bottom Line
Knowing how hot and cold packs work give us a better understanding of why they’re so useful. They each have a different mixture inside of them that makes them work! With a little bit of science, it’s easy to get to the bottom of what makes ice packs so cool.
Propylene Glycol. (n.d.). Retrieved April 21, 2020, from
Hot to Go Reusable Heat Packs. (n.d.). Retrieved May 5, 2020, from
Dynarex Cold Pack. (n.d.). Retrieved May 5, 2020, from
Look Inside a Heating Pad. (2009, May 12). Retrieved May 5, 2020, from
Keen, B. (2018, June 12). What’s in an Ice Pack? Is the Liquid in Ice Packs Toxic? Retrieved April 21, 2020, from
Stankiewicz, K. (2018, June 29). Too many ice packs from mail-order delivery? Here’s how to dispose of them. Retrieved May 08, 2020, from
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