My goal with this was to get something that would create a super cold homemade ice pack that lasted a decent amount of time. I needed this chiefly to keep the bait plugs frozen for my Bait Launcher. I found a few retail available products. Some were reasonable, others were outrageous! It seems they all had one thing in common, they all used some type of hydrophilic polymers in their formulas. So I decided to do some research to come up with the best formula for a DIY ice pack.
Hydrophilic Polymers are those crystals you might find in the garden department that absorb 400+ times their weight in water. They turn into a gel and can slowly release water back into your soil or potting mix. They also dramatically alter the freezing point of water. Here’s a good article that explains hydrophilic polymers and their uses. Hydrophilic Polymers explained.
The Ingredients for a Homemade Ice Pack
My suspicion is that some of the commercially available freezer packs were not just polymer. They all have different phase change temps. Phase change defines where a solid turns to ice and back. There had to be something different in their formulas. I gave this some thought and decided to try a few experiments with items that I knew changed the freezing temperature of water. Limiting the list to items that are readily available was my first goal. The list is pretty short. I ended up using salt, alcohol and propylene glycol as well as Hydrophilic Polymers.
We keep a few containers of kosher salt around so that was a no brainer. Alcohol is easily available. Almost everyone has rubbing alcohol around the house. I ended up using rum though, I didn’t want to put anything in the freezer that was potentially toxic. Propylene glycol is easily purchased at your Local pharmacy. PG is safe, it used as a safe alternative to toxic anti-freeze.PG is also used in vape juice, and as a diluent in the medical and veterinary communities. Knowing this, I felt comfortable using PG for a DIY Ice pack.
Experimentation and Testing
Having figured out what I would use, I laid out plans for my experiment. I did this in three phases. The first phase was to figure out what materials or concentrations would work best. The goal was to see which would stay coldest for the longest amount of time.
I started with various salt concentrations. Salt drops the freezing point of water as does propylene glycol and alcohol as well. I made up batched of the various mixtures in 500ml bottled (bottled water). Conceivably, you can make your homemade ice pack with bottled water containers as well! Ultimately, I chose a different method, but will cover that later.
Each of these mixtures was frozen for a minimum of 24 hours. The freezer I have is good to -5°F so the packs I made up had a chance to freeze to the coldest possible point in my experiments. Next, I tested each of these mixtures over a 24 hour period. I used a remote thermostat in a cooler and a GoPro set for time lapse. This way I could record and graph each of the mixtures temperature over a 24 hour period.
That date was entered into a spreadsheet and graphed. The results let me to one mixture that performed better than the others. The alcohol (rum not rubbing alcohol) mix was the coldest mix. However, it warmed up much faster than the some of the other mixtures. The Propylene Glycol looked extremely promising since it was the second coldest and lasted for a decent amount of time. I decided to test Hydrophilic Polymers in this run as well. Although they look good on the chart, the volume used was large compared to other mixtures. As a result, we can ignore this for now.
On to Phase Two!
In this phase, I used the most promising mixes in a repeat of the last tests. However, there was one key difference. I mixed the two most promising substances in their correct rations and added them to the hydrophilic polymer crystals. Consequently, the mixes I chose were the 10% propylene glycol and the 10% alcohol (rum) mixes. I also tested some retail polymer ice packs in this test run. The results were impressive! The Propylene Glycol and Polymer mix performed extremely well. It reached 13°F and stayed below freezing for 24 hours!
Making a DIY Ice Pack
To make up homemade Ice packs I used mylar bags that can be heat sealed. These are large enough to hold 500ml of whatever I put in them, The basic process is to make the 10% PG mix. I did this by adding 50ml of PG to a measuring cup. Next, I added enough water to the cup to bring it up to 500ml. After that, I added a teaspoon of Polymer crystals to one of the bags, added the water and heat sealed the bag. I ended up making 8 of these DIY ice packs.
Phase Three Test of a DIY Homemade Ice Pack
Now that I had some ice packs made up, it was time to test them. For the final test, I used water as a baseline and froze equal quantities (3 liters) of my formula and retail ice packs. I ran the test again for each of these and found that my mix outperformed the retail polymer based ice packs across the board! Here’s a snapshot of the results. My formula, on average, kept the cooler 10° F colder than the retail Ice packs! Additionally, it kept it below freezing for close to 24 hours!
I’ve made up up eight of the large silver Homemade ice packs. I’ve used these for my bait cooler when I go surf fishing. The idea is to keep the bait slugs for the cannon frozen until ready to use. They have been extremely successful in this. I’ve also made up about 24 smaller DIY ice packs. These are for food. I feel better about keeping the ice packs separate. Even in the best of conditions, some of the bait will eventually leave traces of “bait juice” on the ice packs.
Below is a parts list of some the items I used for this project: