I have a chapter in which my main character visits a cave. And while the air composition is different from Earth’s air, it got me thinking whether he would see a white cloud condensing from his breath.
Hot breath increases the relative humidity of the cold outside air as they mix. Once humidity reaches 100%, it results in breath condensation.
It may seem like a tiny thing when you describe setting & character, but it can provide indirect information to the reader.
If you want to know whether your or your character’s breath will condense into a white cloud in certain locations, you can use this calculator.