Extreme Heat and Cold Rules question

[Phhase]

So, the rules for extreme temperature conditions state that if a creature is resistant or immune to fire or cold damage, it doesn't have to worry about the associated environmental condition. Do you interpret this to mean "Creatures that naturally are resistant or immune," or "Creatures with resistance or immunity from any source,"? It seems a little off for full plate of fire resistance to protect you from desert heat, might just be me though.

[SiCK_Boy]

The source of the immunity should not matter.

Just imagine that full plate triggering its own internal air conditioning when its wearer is walking in the desert.

[JackPhoenix]

Resistance or immunity is the same, no matter how you've got it.

[MoiMagnus]

Let's take fire immunity. If you have an armour that makes you immune to fire, the answer is very simple: there is no way fire damage can reach you, whatever the source. So desert heat is not a problem

Fire resistance is more subtle. What does this mean? Are you half-covered with material that immune you to fire, making it that only half of your body is damageable by fire? Or are you fully covered, but the protection is not perfect isolation so some heat go through it?

Since in 5e, an armour is a single object protecting you completely, every protection is assumed to be total. The suit of armour that give you fire resistance is assumed to protect every part of your body including your eyeballs. Obviously, this is for the sake of simplicity, not the sake of realism. There are some corner cases where this simplified model is immersion-breaking, in which case it is reasonable to stop using the approximation and use ruling adequate to the situation. But those are circumstantial rulings, not rules.
=> The rule is that an armour of fire resistance protect you against desert heat. But taking in account the exact circumstances (which nation created the armour? what was the intended usage? what does this mean on the shape of the armour? how well does it works outside of the intended situations? etc), the DM can rule otherwise.

[JackPhoenix]

Let's take fire immunity. If you have an armour that makes you immune to fire, the answer is very simple: there is no way fire damage can reach you, whatever the source. So desert heat is not a problem

Fire resistance is more subtle. What does this mean? Are you half-covered with material that immune you to fire, making it that only half of your body is damageable by fire? Or are you fully covered, but the protection is not perfect isolation so some heat go through it?

It doesn't matter if it covers you like a complete suit of armor, or if it's a metal underwear. It's literally magic.

[MoiMagnus]

It doesn't matter if it covers you like a complete suit of armor, or if it's a metal underwear. It's literally magic.

But it does depends on what part of the body the protection against fire protect you against. Maybe the magical armour make a force shield around you that protect you against fire, and just having a magical underwear is enough (which is probably what you're having in mind). Maybe the magical armour is just made of a magical metal which is a perfect thermal insulation, which mean that if you are totally covered by the armour you get magical resistance, but if you just had an underwear it would not work as fire would go around.

Rule-wise, both would be "armour of fire resistance", except that one requires you to be completely covered and the other not. It just depends on how the magical armour has been created, and WHY does the armour protect against fire damage (with more details than just "a magician did it": what kind of magic was used, etc).

[JackPhoenix]

But it does depends on what part of the body the protection against fire protect you against. Maybe the magical armour make a force shield around you that protect you against fire, and just having a magical underwear is enough (which is probably what you're having in mind). Maybe the magical armour is just made of a magical metal which is a perfect thermal insulation, which mean that if you are totally covered by the armour you get magical resistance, but if you just had an underwear it would not work as fire would go around.

Rule-wise, both would be "armour of fire resistance", except that one requires you to be completely covered and the other not. It just depends on how the magical armour has been created, and WHY does the armour protect against fire damage (with more details than just "a magician did it": what kind of magic was used, etc).

That's not how it works. There's no "fire resistance, but only on body parts covered by armor". You either have resistance, or you don't.

[MoiMagnus]

That's not how it works. There's no "fire resistance, but only on body parts covered by armor". You either have resistance, or you don't.

The rules don't describe accurately the world in which the RPG takes place. Their approximate it to give to the DM a simple way to resolve actions. And fire resistance being a "you have it or you don't" is an approximation because in 99% of the case there is no reason to have more precise rules than that. In 99% of the time, you don't care about what are the internal magical behaviour of the armour, how it affects the weave to protect you against fire (do you still feel heat and just suffer no damage? do you have have an aura of coldness around you? what part of your equipment is protected by fire and when does an object you hold stop being considered as part of your equipment? etc).

[Zhorn]

MoiMagnus, it sounds like your overthinking this trying to insist upon extra complexity which the rule for extreme heat and cold don't call for.

[Mastikator]

If the magic armor of cold resistance magically protects you from Snilloc's Snowball Swarm then I don't see why it wouldn't also magically protect you from an a snowstorm the same way.

[Rusvul]

RAW, it's pretty clear that any resistance or immunity works.

But if my DM rules that my nonmagical dragonskin leather armor didn't protect me from extreme heat, I wouldn't complain--that makes sense, if or conceive of the armor as physically shielding me from, like, fireballs and similar. Thinking about it from a real-world perspective, fireproof armor wouldn't necessarily help against ambient heat the same way a spell or innate adaptation would.

There is room in DM rulings for nuance beyond what is explicitly called out by the rules as written, and I think that's what MoiMagnus is getting at.