I have my favorite 40oz. stainless steel insulated tumbler, that seems to insulate in reverse...

It actually works better when it's warmer than when it's colder, and by "it's" I mean the ambient temperature surrounding my personalized, heavy metal big gulper. Can somebody please 'splain it to me why this happens? My undrunken liquids stay colder longer/ice melts slower when it's above 68º than when it's below 62º inside the abode... the former being what I consider warm inside, the latter is my cool/cold zone. Most of the year here it is closer to warm, and the duration of cold/icy is predictable within my comfort zone. It just seems weird that when it's above or below my comfort zone, the contents perform in the reverse of what's expected.

Somebody's gotta know why, and Sheldon isn't responding to my texts and emails today, as it seems the pending end of his show is more emotionally draining than expected.
Thanks.
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Not sure I understand the drink temps versus the air temps.

General performance of stainless mugs is that they keep things cold longer than they keep things hot. Cold tends to flow down and hot tends to flow up. With a plastic lid on the mug, water molecules from the warm drinks tend to evaporate from the liquid and condense on the lid and warms the lid. The lid has much poorer insulation properties and conducts heat out of the container. This is why warm drinks don't hold temperature as well as cold drinks (assuming there is no ice in the cold drink).

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In tha 360. MRF User Map

Putting more ice in when hotter .

I even keep a neoprene koozie on the bottom of the tumbler for add'l insulation. It's a conundrum. I never do hot drinks, so that's not an issue. It's either unsweetened iced tea, flavored sugar-free bubble water, or watered down Powerade, or worst case, plain filtered water. No matter the liquid among them, all fare better longer when it's warmer inside our home.
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So it's all drinks without ice? Do you have a lid on it? What are you using to record the temp of the liquid?

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In tha 360. MRF User Map

Always start w/ ice. Lid is always on. No actual thermometer, but much less ice remains next day when cold ambient temps than when warm, and remaining liquid seems colder when there's more ice left. Also, sometimes just for shiggles, I'll occasionally let the tumbler melt down to near nothing before refilling, usually when changing potions inside, and it takes longer to do so when warmer.
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Actual temperatures would be helpful.

Without them it might be a matter of perception.

The lovely cooled beverage's temperature stays the same, but is noticeably cooler when the ambient temperature is warmer.

In cooler ambient climate, the difference is between the two temperatures is less noticeable, so as the lovely beverage loses some of it's initial big chill, it's more readily perceived as not staying cool as long, even though the rate of warming is almost identical.

It actuality, unless it has very good insulating properties, it will allow its contents to warm more quickly in a warm ambient climate than in a cool one.

At least that's my guess, being more or less ignorant of thermodynamics.

OR — the ice simply fights harder when it's hot outside and gets lazy when it's not.

Maybe you should try using heavy water.

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It would help if you could standardize things: use distilled water and freeze a specific volume (and shape) of water, make sure the ice in the freezer is the same temp, put it in the tumbler with a known volume of distilled water at a specific temp, then weigh the ice (or measure water's increased volume) after so many hours.

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In tha 360. MRF User Map

The best I could think of was some sort of temperature deviation in the initial ice, and/or liquids. The ice comes from store bought ice bags from the same freezer. Some liquids came out of the fridge, some didn't, but my brain says they all normalized by bedtime. It's the difference between bedtime and the following day where the conundrum manifests... from mid-day thru the evening, I'm powering down lots of fluid. The mass hydration varies day by day, so it's the overnight time on the kitchen counter that's in play.
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so it's the overnight time on the kitchen counter that's in play

Let me guess, this is a stone (granite/marble) or quartz counter top?

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39°36'17"N 75°44'43"W

The search engine that doesn't track you.

I think you answered this in your title. It’s ghosts.

But seriously, this is not so much a matter of temperature, as it is of time dilation. Einstein wrote of this in his theory of relativity. Time will move more quickly in a warmer room versus a colder room. He also theorized that ice was an anomaly not affected by this phenomenon, and time would progress for it along the base timeline that was established while it was formed in deep space before it even became a part of the planet billions of years ago. Funny enough, the time dilation effect (or TDE) is most pronounced between the temperatures of 288-294 detrees Kelvin. I think this is what you’re seeing in your tumbler. Just make sure you do not test this effect in your Delorean traveling at more than 88mph. The results could be disastrous.

MrNB- It's a laminate countertop that only looks like crushed quartz... and the other fave stash place is on top of the table that has a thick pad on it, covered by a tablecloth. Plus, as noted, the tumbler has a neoprene koozie that covers the bottom.

BD- That's exactly what I was afraid of...
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