The old fridges that didn't self-defrost are probably the most reliable. The only moving part is the compressor. No fans, no heaters, and fairly quiet. But the freezer compartment will ice up especially in humid climates and must be periodically defrosted which is a bit of a PITA.
Defrosting sucks profoundly, also the frost build=up makes opening drawers hard and prone to damage. Additionally it takes another fridge to store the contents.
have there been improvements to the insulation? given how good high-end coolers are now, i'd assume that there's been something with the non-mechanical parts that could have improved
Ultimately, not much. The polyurethane insulation of 1995 is pretty comparable with the polyurethane insulation of 2025.
There are better insulations out there, but they cost money and are harder to work with. For example, we could theoretically vacuum seal a fridge, but that'd require an airtight seal and likely a stainless steel structure around the fridge.
I think a lot of coolers used to have some parts like lid or even sides that were simply double-walled with an air gap and no real insulation. I remember old internet posts about people enhancing theirs by drilling into these spaces and injecting them with a minimally expanding foam from the hardware store.
Maybe somewhat better insulation and then I have noticed with combined units that there is more of it. That is usable volume is smaller due to larger amount of insulation.
Is that true though? Better coolants, inverters / variable speed / scroll /swing compressors, insulation and mfg, etc. maybe for residential it’s less impactful, but refrigeration in general has better efficiency than 30 years ago.
The Montreal protocol (1987) put us back into the dark ages with coolants for a while (both with CFC ban and later phase outs of HFCs). I suspect if you tested a refrigerator from 40 years ago they would give modern ones a run for their money...
It was obviously a worthwhile sacrifice for the ozone layer though.
