Insulin Cooling Battles: Frio vs Breezy Packs

My previous battle, Frio vs Gel, showed that while a gel pack slows down the transfer of heat, it has no power to stop that heat energy eventually reaching the contents of the pouch. In contrast, the evaporation of the water from the Frio pouch actively fights the heating of insulin by redirecting the heat energy to converting the water from a liquid to a gas.

In this battle, we have two related, but different technologies which both redirect the heat energy to perform other tasks than heating the pouch contents. As mentioned, for the Frio pouch, it is the conversion of water to steam and, for the Breezy Pack, it is the melting of a mysterious substance called a PCM (Phase Change Material).

What are PCMs?

We know from high school science that, in the everyday world, matter is in one of three states: solid, liquid, or gas. What we may not know is, to move from solid to liquid, or liquid to gas takes energy. The scientific term for the energy required to melt a substance is the “Heat of Fusion” or “Enthalpy of Fusion” and it is measured in energy per weight e.g. kJ/kg or energy per volume e.g. MJ/m^3.

The energy needed to evaporate a substance is called the “Heat of Vaporization”. It turns out the energy needed to evaporate water is really high. It literally takes five times the energy to get water to turn to steam once it reaches boiling temperature than it takes to take water from ice to that temperature. So, if you have a kettle or heater which can get your water to just under boiling temperature, and that serves your purposes, do so because you will save a LOT of money on energy bills.

So, in the case of our Frio pouch, the PCM at play is water going from a liquid to a gas. While water does boil at 100C (212F), even at 30-40C (86-104F) we get some cooling effect because the water molecules in the Frio pouch are at a range of energy levels so a little heat energy can tip some of these over to becoming a gas at these lower temperatures. This is why we may see a little steam, even before the water is boiling.

In the case of Breezy Packs, the makers do not reveal what the PCM substance is but we can make an educated guess.

What is the PCM in Breezy Packs?

This is what we know:

  • The substance is solid below 25C (77F) and turns to a liquid above this temperature. We know this from the instruction sheet.
  • From the Breezy Pack website, the substance begins to melt above 27C (80.6F)

Going to Wikipedia, we have a range of common PCMs. Assuming the manufacturers have gone for an inexpensive PCM whose melting point is somewhere above room temperature and below the fail temperature for insulin (around 30C/86F) the obvious choice is Sodium Sulfate, maybe with some salt added. At US5c/kg, it is the cheapest PCM in the table, after water. You will notice below that pure Sodium Sulfate melts at 32.4C (90.3F) but, adding a little salt brings this down to a lower temperature. I have bought some pure Sodium Sulfate to experiment with and see if I can replicate the Breezy Pack but that is for another post.

The Experiment

As with the Frio vs Gel experiment, I have enlisted the help of my oven to maintain an even temperature. While I used the middle shelf and the fan forced setting last time, I was finding the oven was going above 46C (115F) which I did not want so I put the Frio and Breezy pouches on the lower shelf with only the top element on. I also put a dishcloth on the middle shelf to act as a shield from the direct heat of the heating element. I also put the two pouches on two plastic cutting sheets to prevent contact with the metal bottom.

The wires were linked to digital sensors so I could monitor the temperature.

The blank one is the temperature of the oven.

The Breezy Packs, at the time of writing come in two versions: Breezy Basic and Breezy Plus. Both of these are the same physical size but the Breezy Plus contains more PCM so it can work for longer. This experiment used a Breezy Basic. The Frio pouch was the same one as I used in the Gel comparison and was soaked in water for the same amount of time prior to going into the oven i.e. 5 minutes. The only difference was the temperature of the water used which, in this case, was room temperature and not, as last time, from the cold tap.

The Results

So, for an oven where we the temperature is between 35-40C (95-104F), we see that the Frio took around 15 minutes to go from 25C (77F) to 30C (86F). In contrast, the Breezy Packs only moved 1.5 degrees Celsius over the same time period.

The rapid rise in the Frio surprised me as it took twice as long to move the temperature the same distance but, even if we use the Frio vs Gel pack results for considering the Frio pouch, we see that it is still out-performed by the Breezy Pack. My guess is the sensor in the Frio pouch was closer to the outside this time around and, therefore heated up quicker. An alternative explanation could be the difference in oven temperature from last time changing the performance of the Frio pouch i.e. the oven ran a little hotter, although more consistently this time around than last time.


To my initial surprise, the Breezy Pack strongly outperformed the Frio pouch. In hindsight, this makes sense. If we think about it considering the PCM in each case, for water, most of the water molecules are still too cold to transition to a gas state and, therefore the heat energy is simply used to warm the material. For the Breezy Pack though, the majority of the molecules are close to melting and will more heat energy can be redirected away from heating the pouch.

Given the Breezy Pack requires no soaking, is not damp and simply works and given the price point for both the Frio pouch and Breezy Pack are similar, it seems clear the Breezy Pack is the superior option between the two when carrying a couple of pens.

Please note: I bought all pouches with my own money and have received no financial benefit in this comparison. This being said, I am very, very open to receiving sample pouches if either Frio or Breezy Pack want me to compare different sized models in the future 😉

7 thoughts on “Insulin Cooling Battles: Frio vs Breezy Packs

  1. Eyal December 21, 2021 / 2:40 am

    Hi Leon!
    I absolutely love seeing our products put to the test.
    We put a lot of thought into their design, and after the extensive testing they undergo in our lab, I’m not at all surprised at the results.

    Great explanations about the physical mechanisms at play. Just one comment-

    You’re right in saying that inorganic (salt-based) PCMs are the cheapest option, but wrong to assume we went for the cheapest ;).
    Salt mixtures like you describe tend to degrade over time due to phase separation, and we want our products to last as long as possible, even if that means somewhat higher production costs. Furthermore, These mixtures also often contain metallic salts that can have negative environmental influences when disposed of.

    All the best
    Eyal from BreezyPacks.


    • leontribe December 21, 2021 / 3:30 am

      Hi Eyal,
      Thankyou for the clarification on the type of PCM used (even if the specific material used is still secret :)).
      I had read about the degradation in using inorganic PCMs and it is great to hear you have not compromised quality for profit. I am really looking forward to the larger Breezy models being released. I genuinely believe they are going to be a game-changer for people who need insulin on the go.


  2. Kirsten May 9, 2022 / 11:07 am

    Thank you for reviewing these travel packs. Our family is new to all this so it is very helpful! My son is going on a two week camping trip soon and I was very stressed until I read about these great options!


  3. Dev May 13, 2022 / 10:58 am

    Hi Leon!

    Thanks for your post. I’m really interested in the topic, as I’m trying to prepare for my first summer with T1D. I’m really surprised by the discrepancy between what’s being advertised and what you see in your tests. FRIO officially claims to maintain the temperature between 18-26°C, while BreezyPacks promise to keep “under 30°C”. And yet, in your test, BreezyPacks somehow manages to outperform FRIO by keeping a lower temperature.

    The difference might seem insignificant, but it seems to be, that for some insulin brands manufacturers declare 30°C as an upper limit and 25°C for others. Even with the room temperature around 22°C I’ve noticed, that effectiveness of my rapid-acting insulin fades away over time even in a two-weeks interval, so I’m really reluctant to go above a recommended limit even though I realize there still might be some headroom.

    I’ve tried to reach out to BreezyPacks, to clarify if they can provide more details about in-case/environment temperature correlation, but they failed to respond in any way. Based on official statements, I was going to by FRIO, just to be safe, even though I find an idea of self-rechargin non-moist case much more compelling. But your post rekindled my interest to BreezyPacks.

    I wonder if your tests could be a little longer, something tells me, that 20 minutest is hardly enough to see all the nuances, that could surface if the product would be used throughout the day. I’d say 1,5-2 hours would be a reasonable starting point.

    I also, wander if you plan any posts on portable coolers for insulin that is not currently in use, like mini fridges or ice-pack coolers that would allow have some spare insulin during longer trips, in case case I my main supply still somehow manages to spoil? I did some market research on the topic, so I know brands “in the game”, but most reviews seems to get those samples directly from manufacturers ans fail to provide some actual temperature measurements, instead just constantly praising those products. Diabetic products are priced quite high and insulin prices are even higher, so I’m not really looking forward to taking any chances, especially with something my life is relied upon.

    Thanks for you great work.


    • leontribe May 13, 2022 / 5:15 pm

      Hi Dev,
      Thank you for the post and kind words. I am hoping to get my hands on a Vivi Cap soon and will run all three against each other. My oven’s minimum temperature is around 50C which accelerates the internal temperature but I can try and bring this down a little to extend the length of the experiment. In terms of other devices, I am happy to test anything I can get my hands on. If you know of any manufacturers looking for a blog review, send them my way 🙂

      David Burren also blogged on his experiences with insulin sitting in the 32-35C range ( which may be of interest.

      In terms of the performance difference between the Frio and Breezypack, another factor which may be coming into play is the enclosed nature of the oven. As the Frio relies on evaporation, this will become harder as the air in the oven becomes more humid. This may be giving Breezypack an edge in my setup but not necessarily so in real life. The next time I test I’ll probably keep the oven door slightly open to cool the temperature and also allow the air to dehumidify.


      • Dev May 14, 2022 / 3:50 am

        VIVI Cap indeed has a very interesting compact form factor and also provides cold insulation, that is a quite unique feature on the market. Though, it has some known drawback as well:
        – you need different caps for different brands and even then it might not fit perfectly;
        – indicator battery is not replaceable, so when it dies, you can’t check if it still cools properly. Manufacturer claims that a battery will hold charge for years, while users report a much shorter performance;
        – you can’t use if a needle is still on a pen (probably the biggest issue).
        And then there is the price… I’m not trying to dissuade you as I don’t have any first-hand experience with it, just some points to look for during review. I would be very interested in seeing performance comparison with other options on the market.


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