Not sure if you will see this reply considering the age of the thread, but I have a follow-up question to you reply: I recently bought two types of Arctic Ice brand freezer blocks, one freezes at 28.4ºF one freezes at 5ºF, would it be better to use one of each, so the state change occurs at different times as the contents warm (say over 2 days) or 2 of the same, so that the state change occurs at the same time but takes more energy?

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Dear timewethink:

On Tuesday, August 9, 2022 at 7:45:05 AM UTC-7, timewethink wrote:
> I recently bought two types of Arctic Ice brand freezer blocks,
> one freezes at 28.4ºF one freezes at 5ºF, would it be better to
> use one of each, so the state change occurs at different times
> as the contents warm (say over 2 days) or 2 of the same, so
> that the state change occurs at the same time but takes more
> energy?

Your insulation system is unlikely to perform well with 5°F "ice". So mostly that one gets shot first, with a much higher heat rate from ambient.. Contents are colder... 'extra' cold does not buy you any better food protection.

Maximize insulation, minimize temperature difference.

I also had a crappy "cool bag" that I somehow thought was "water proof". The ice was melting, and the water was dripping out the bottom... so it could not conduct / convect heat to the walls of the "cool bag". One bag of ice lasted for almost a day, and food was cold the entire time. Don't get that with the typical styrofoam cooler.

David A. Smith