Explanation of how it will work

• Now we have block temperature and also armour temperature that can be either positive or negative.

• Suppose we have hay bale configured to have -1 block temperature. (Like because it is insulating)
  And suppose we also have a straw hat that has -1 armour temperature.

If there are warm temperatures, then it's fine. But if there are cold temperatures, then it's not as intended. Because hay bale and straw hat no longer "insulates" like. Instead of they are cooling you down. But that's not a problem if you have...

Relative temperature

• If the player's temperature is negative, it will be shifted positively.
• If the player's temperature is positive, it will be shifted negatively.

This means that '12' (The most comfortable temperature) will be the centre. Anything lower than '12' is negative. Anything higher than '12' is positive.

24 > 12 > 0
Too warm > Optimal > Too cold

So, if a block has relative temperature 1, it'll check if playerCurrentTemperature > 12. When this is true, the temperature will be raised 1 down. If this is not true, then it will check if playerCurrentTemperature < 12. When this is true, the temperature will be raised 1 up. And if this is not true nothing will happen.

This will solve this whole insulating problem and might solve some extra problems. (For example compatibility with Advanced Rocketry. Spacesuit will always keep you away from all kinds of temperature differences on all kinds of different planets.)

• Also, you could insulate your house with hay bales. And became safe from the temperature in all kind of seasons.
  MrCrayfish's shower and bath could also have a relative temperature. But that's on how - who will configure it.

Hope I explained it clearly! I think many modpack makers would enjoy this powerful feature. (not just me)
And finally, thanks!

It's a bit tricky... there is a "relative" system that can be worked with called "dynamic modifiers", just that lots of new stuff would have to be written to interface with it.

Support for armor would need a new json format that includes the "optimal" temperature, which isn't too bad, just would take a bit of work.
Right now there's some support for armor via "Armor Underwear", you could add that mod then add its liner tags to things like space suits and it'll work like you expect, although a proper configurable one would be better.
You can see those tags in AUWDynamicModifier in this repository.

Blocks on the other hand are really tough, as there would need to be a new dynamic modifier that checks for blocks around the place, which is pretty laggy.

If you want to try adding any of these for yourself in the fork, you just have to make a class that extends ITemperatureDynamicModifier and add the modifier with TemperatureRegistry.registerDynamicModifier

I can try to look at doing these officially if you're still interested in these, but I unfortunately can't make any promises, I've been really busy for the past year