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pvtdirtpusher t1_irezj2n wrote

As said by others, the opening and closing is the killer. Not only are you exposing the contents of the thermos to air in the short term, you literally taking hot liquid and replacing it with room temperature air. Meaning that the thermos has both less thermal mass ( an subsequently easier to heat up) but now has to equalize in temperature with the room tell air now inside the closed thermos.

Fully primed, filled and left untouched,, I would expect it to last close to full time they specify

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gravitas_shortage t1_irf0gpk wrote

Worth a test. My hunch was that unless the bottle is left uncapped for extended amount of time, it should not fall that quick, but then the smaller model has only half the expected hotness time, so maybe thermal mass is that important for a thermos bottle and I'm just capping my ignorance with more ignorance and should withdraw from this thread and perhaps civilisation altogether.

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Loobeensky OP t1_irf1gua wrote

Half the expected hotness time? I splurge to have the most effective thermos and that's what I get? What a disappointment.

(I'd be more than satisfied with 28–30h of properly hot water though.)

Now I wonder if their "indestructible" model performs better.

The expected temperature retention goes up with the size of the bottle, so I had big plans for this boi.

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gravitas_shortage t1_irf25st wrote

It can go two ways:

- Thermal mass is a major factor.

- The ratio of surface area to volume in a big bottle is much smaller, so the heat loss is much smaller.

Both ways can be true and act in opposite directions.

We need thermal measurements over time and volume, OP. For Science.

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gravitas_shortage t1_irf6hhz wrote

Also, I'm glad to report that I just checked, and it is not the case that there is a point of emptiness at which the larger bottle gets a smaller volume-to-area ratio than the smaller one. So, no need to get a smaller bottle depending on your expected consumption in order to preserve the heat. Whew.

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Loobeensky OP t1_irf0f3s wrote

Thank you for you answer! Yeah, that makes lots of sense. Time for some proper testing without opening the bottle.

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