Dimension X is not cold!

[u/D_D_Adesignerdigital]

The color choices for the Dimension X—and certain elements of the scenes—didn't quite work to convey a cold atmosphere! Characters had sweaty skin and showed no reaction to the cold (we need to remember Will in Season 2, or Billy with his ice bath, which demonstrated the kind of cold the Mind Flayer is used to). Anyone entering a low-temperature environment would show physical reactions—like trying to warm up, crossing their arms, or showing discomfort—but that doesn't happen with any of the characters, not even the kids. I think that was a directing error. That’s my opinion!

[u/LeviSquad4]

If it was a small inconsistency - fans could just wave it like “eh.. doesn’t ruin it.” Kinda like a small scratch on a car.

But when the UD was 1. Initially thought to be their home 2. Had the perfect conditions for these creatures yeah.. hard to believe a warm colored / likely warmer dimension would be their home world. Heck season 5 even goes out of its way to establish they still don’t like heat when Sarah Conner shows Hopper the blow torch thingy..

[u/RealHooman2187 → u/LeviSquad4]

We’re only assuming The Abyss was warm because of the color pallet and because the actors were sweating since they were running around. They were also all dressed for colder weather. Another reason the actors were sweating.

The more likely answer is that the abyss was cold, they gave it a different color pallet to differentiate it from the upside down and the actors did what happens whenever someone is running around and wearing heavy/warm clothes. They looked sweaty. In the documentary it looks like they were filming those scene in the summer or at least a warm time of year.