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For context

One of my players is playing for the first time and has some problems with magic and how versatile it is, therefore he is attempting to make an armor to resist fire, lightning, acid and cold. Of course, he is not using any magic. He is a bit more knowledgeable than me in how physics work and likes to apply them ever since I said that in D&D you can try to do almost anything.

How it presumably works

His idea is to make a wool based gambison knee length covered in copper plates and copper wire. The idea is that he the wool would insulate from heat and cold, the copper plating would protect the wool from catching fire and would also provide protection against acid. Finally the copper wire would have a hook to stick in the ground and would serve as a lightning catcher completely protecting against the damage. All of that worn on top of a full plate armor.

That is obviously broken.

I don't want to allow him to make it without major draw backs but I don't want to say no completely either. I don't even know if it makes any sense at all, what he is trying to make.

I am new at DMing.

Is it possible to get magical elemental damage resistances through mundane means?
What would his project cost (time and money) how hard would it be to make? Should I allow it?
What are the implications?

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    \$\begingroup\$ Hi HNQ visitors! I would just like to remind you that comments are not for answering the question. If you have advice to solve the problem, please put it in an answer below along with the support to back it up. \$\endgroup\$
    – Someone_Evil
    Jul 14 at 11:52
  • \$\begingroup\$ @Carson We should avoid even partial answers in comments, see here: Should users refrain from answers (or partial answers) in comments? \$\endgroup\$ Jul 14 at 16:19
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    \$\begingroup\$ @Mike Can you clarify, is the player actually shunning magic (i.e. their character refuses to wear magical items) or is the player just irritated that magic can do so much that mundane items can't? \$\endgroup\$ Jul 14 at 20:30
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    \$\begingroup\$ "He is a bit more knowledgeable than me in how physics work" - the player, or the character? Assuming the player is the knowledgeable one, how does his character know how to build this? \$\endgroup\$
    – tardigrade
    Jul 15 at 6:44
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No, this scheme does not work. Elemental magic is primarily magical rather than primarily elemental

For the same reason you can successfully cast Fireball underwater you can't expect wool and copper wire to mitigate a magic spell's damaging effects. It's often said that D&D is not a physics simulator, and this is one of the cases where that is relevant. This means that, for circumventing game rules, your player's knowledge of physical science is irrelevant.

Other details arguing against this idea exist but are less important than the above reason, which is decisive. You may or may not want to give some benefit for creative thinking, but full-on resistance is a pretty big deal and is generally gained by making some significant investments towards it rather than in other options.

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    \$\begingroup\$ Although being underwater grants resistance against any fireball's damage. So maybe you could pick another example? \$\endgroup\$
    – STT LCU
    Jul 13 at 12:59
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    \$\begingroup\$ @STTLCU I see what you mean, but Fireball is the canonical example (complete with a Crawford statement). The point is less about resistance to fire damage (a resistance that only exists because the rules specifically state that it does) and more about there not being any interactions between a giant magical fireball and water in which it is totally immersed: the water doesn't evaporate, the fireball's range isn't reduced, etc. The "realistic" interactions one might expect just don't occur, it's all about what the rules specifically describe. \$\endgroup\$
    – Upper_Case
    Jul 13 at 14:40
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    \$\begingroup\$ @STTLCU if you want a few other examples...lightning dissipates very quickly when it strikes water--but Lightning bolt has its normal range and behavior. Extreme heat (like being in a volcano) has no effect at all on the function of ice magic--sleet storm can create and sustain an ice slick anywhere, nor does arctic clothing offer any protection from cold damage. And lightning spells do not consistently work better on an individual covered in metal. Shocking Grasp gives you advantage on the attack if they are wearing metal--but very few other lightning spells gain such a benefit. \$\endgroup\$ Jul 14 at 17:48
  • \$\begingroup\$ A dodge save halves damage from fireball also. I don't think that's how physical fire works, and especially for anything that is close to an actual ball of fire and has a 20 foot radius. \$\endgroup\$
    – Nelson
    Jul 15 at 8:13
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It wouldn't work even if D&D was a physics simulator

I second everything that Upper_Case and ThomasMarkov have said, but there's another problem. Even if D&D were a physics simulator, this wouldn't work in practice.

Wearing a contraption like this would likely cause the wearer to have serious issues with heat just walking. You are talking about putting a heavy, special gambeson on top of plate armor. But remember that historically plate armor was worn over a gambeson already. DND honors this in its description of plate armor by noting that the metal is worn over "thick layers of padding". D&D avoids the word gambeson, I suspect because most people don't know it, but that description basically matches a historical gambeson usually worn under plate armor.

In other words, to the extent a gambeson could protect you from magical heat or cold, its already built into plate armor. Adding more won't really help and even if it did it would come at the cost of making an already heavy, hot, and bulky set of armor even heavier, hotter, and bulkier. (I am well aware that modern recreations suggest that plate armor is much less encumbering than an average person thinks, but it is still encumbering and that is for well fitted armor, not for armor that has extra layers of padding jury rigged on the outside).

Setting up the armor as a grounded faraday cage type of arrangement might actually work. That basic setup is why it isn't a big deal when lightning strikes an airplane which happens on a regular basis. There are also interesting videos of of people wearing a faraday suit and interacting with Tesla coils in real life. But, there are problems with the proposed setup even if we ignore the fact that, as Upper_Case correctly noted, magical lightning shouldn't be treated as real lightning.

Namely, a lot of things would have to go right. There would need to be an unbroken line from where the lightning hit to the ground through the armor and there would have to be no place where there was an easy path form the armor to the skin. This definitely can happen, but that's a lot to ask in a chaotic battle even with modified armor.

A possible compromise?

Still, you want to encourage him to be creative and to be involved in the game, without adding things that are game breaking.

If I were ruling as a GM, I might say that modifying plate to act as a Farady cage would cost 4,000 gold. This would give resistance to lightning only. The modification is incompatible with having the armor be magical so it can only be done to mundane armor that cannot later be enhanced.

That number is somewhat arbitrary, but the way I am looking at it is that a ring of resistance is worth around 5,000 gold. You are giving him the equivalent ability, but without making him use up either a ring slot or requiring attunement. But that doesn't matter much if he doesn't have any rings or items that require attunement. So, we trim the price by about a thousand as a further reward for creativity.

You are letting him run with his fluff and giving him a discount for creativity without letting him have something game breaking.

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    \$\begingroup\$ For a physics simulation, remember people need to dump heat. If they can't, they boil themselves up. So physically cold resistant armor would kill its wearer when not subjected to any cold, or worse, attacked with heat. \$\endgroup\$
    – Mołot
    Jul 12 at 22:28
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    \$\begingroup\$ It sounds like the player wants to cover a layer of meticulously crafted high quality steel with heavy and grabby copper and wool. If this were a physics simulation, I'd tip the poor fellow over, or stick his amazing velcro armor so full of projectiles that he'd tip over himself. \$\endgroup\$ Jul 13 at 9:33
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    \$\begingroup\$ I like your answer. It rewards the creativity and the thought that went into it without allowing any game-breaking behavior. Also very sound reasoning \$\endgroup\$
    – Hobbamok
    Jul 13 at 10:21
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    \$\begingroup\$ @Mołot That's valid if we're talking about long term wear in an arctic or desert environment, but for the purpose of combat spells, fire and ice and acid are all kinda the same: if it touches your skin, it hurts. A blast of fire or cold comes and goes in a matter of seconds; there's not enough energy transfer there to change your core temperature. It's the skin damage you need to worry about, so coverage is more important than anything else. \$\endgroup\$ Jul 13 at 18:06
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    \$\begingroup\$ @TimothyAWiseman On the compromise -- Isn't this functionally equivalent to an armor of resistance (also a rare item) that doesn't require attunement? I don't think it's kosher to remove one of the major limits on how many magic items you can have on you and also cut the price. \$\endgroup\$ Jul 13 at 18:10
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An item granting four damage resistances is an extremely powerful item.

Upper_Case's answer has all you really need to come to a ruling here, but I think we can motivate that answer further by comparing the proposed item to existing magic items and magic item guidance. There are already two magic items that grant damage resistance, the Ring of Resistance and Armor of Resistance, and these each grant a single damage resistance, and are "Rare" magic items, valued at 501 - 5,000 gp. If damage resistance were as simple as following some mundane design principles with mundane materials, we wouldn't have magic items filling the same role that cost astronomically more than a warm coat.

An item granting four damage resistances is possible, but only under extremely unlikely circumstances. It is possible under written guidance, for a DM to create a magic item that does exactly as you describe, granting four damage resistances, and that is by creating an Artifact:

An artifact is a unique magic item of tremendous power, with its own origin and history. An artifact might have been created by gods or mortals of awesome power. It could have been created in the midst of a crisis that threatened a kingdom, a world, or the entire multiverse, and carry the weight of that pivotal moment in history.

[...]

Characters don’t typically find artifacts in the normal course of adventuring. In fact, artifacts only appear when you want them to, for they are as much plot devices as magic items. Tracking down and recovering an artifact is often the main goal of an adventure. Characters must chase down rumors, undergo significant trials, and venture into dangerous, half-forgotten places to find the artifact they seek. Alternatively, a major villain might already have the artifact. Obtaining and destroying the artifact could be the only way to ensure that its power can’t be used for evil.

Artifacts represent the most powerful magic items ever created, and are totally unique. When introducing an atifact into the campaign, the Dungeon Master's Guide suggests assigning some random properties to the item:

An artifact can have as many as four minor beneficial properties and two major beneficial properties. It can have as many as four minor detrimental properties and two major detrimental properties.

One such minor beneficial property is:

While attuned to the artifact, you have resistance against one damage type of the DM’s choice.

With a 10% chance of rolling this property for an artifact taking 4 minor beneficial properties, there is a 1/10,000 chance an artifact could have the properties proposed in the question.

Basically, your player has asked to create one of the most powerful magic items in the universe out of mundane wool and copper, that a Dungeon Master can expect to create themselves in only 1 out of every 10,000 campaigns where they happen to create and implement an Artifact item having 4 minor beneficial properties. As you say,

That is obviously broken.

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The game being about "almost anything" is the issue

You said "in D&D you can try to do almost anything", and this is probably the underlying issue which should be addressed. Don't get me wrong, D&D is indeed a game of imagination. Unlike conventional board games, D&D does not limit players by a specific list of choices. The PHB makes accent on this several times:

Your character can do things not covered by the actions in this chapter.

You're not bound to those options, but they're a good starting point.

You just need to aspire to create, to have the courage of someone who is willing to build something and share it with others.

PHB also says that

The only limits to the actions you can attempt are your imagination and your character's ability scores.

Without context, this can be misinterpreted as "everything is possible". But it's not the case. The DM always sets the limits. The same paragraph says that explicitly:

... the DM tells you whether that action is possible

When you getting acquainted with your first game system, it's easy to fall for the illusion of its omnipotence. You think you can simulate any kind of situation, and the game system itself will magically make it playable, as long as you follow the rules. This is a common mistake made by new DMs. The game system itself doesn't have any magic. It's the DM who does the magic.

D&D ruleset is just a toolbox which is limited by design

The rules don't explicitly say what you are supposed to do, but they give you a tool. And "if the only tool you have is a hammer, it's tempting to treat everything as if it were a nail". The Three Pillars of D&D are Combat, Exploration and Social interactions. Anything out of this scope (like, making contraptions) has little to no mechanical support. You can still do that, but the game system won't offer any help. Trying to squeeze D&D ruleset into solving problems out of its scope would be like unscrewing a screw with a hammer.

Every D&D game assumes a genre, and genres differ

Albeit DMG assumes different genres, a particular game should be about something specific. Being about anything is the same as being about nothing. 5e is a game of cooperative storytelling, and following different genres produce different stories — a gritty survival horror scenes won't suite a lighthearted comedy, and vice versa. Using a faraday cage stuffed with wool in real combat is like carrying a stepladder for fighting giants. The latter has strong comedy flavor which might not suit the rest of the game.

At the end of the day, it's about reaching a consensus

When we're talking about what is possible in 5e, we're mostly talking about what people believe is possible in this particular game world. The game system give us guidelines, but it doesn't actually say what is possible and what is not. For example, the woolen faraday cage should render the wearer almost completely immobile. You wear a gambeson, a plate armor, then you wrap yourself in thick layers of wool, then you cover this with copper plates which should be connected and grounded. I can't imagine anyone could even normally walk with all these things. But this is just my opinion. If the rest of the table disagree, I'd rather support the consensus.

For combat mechanics, stick to the published materials for now

Combat is a huge part of any D&D game. It is the main focus of the game system, it's also the primary subject of the game balancing. Adding "+3" to someone's sword too early could negatively affect other players' experience and make the game less enjoyable.

The same is true for damage resistance. An item which gives you resistance to multiple types of damage is very powerful in terms of game mechanics. Allowing mundane means to be as powerful as legendary artifacts opens a straight way to abuse.

If you're a new DM, I suggest you the following. Instead of homebrewing new things or introducing new mechanics, try reskinning things from existing published materials. And if you can't, just forbid the abuse: "I agree this sounds reasonable, but this will break the game, so I can't support this in terms of mechanics".

It's tempting to invent things on the fly — "I cover my daggers with dung to infect my enemies' wounds" — "wow, that's smart! now both daggers deal +2 damage and afflict Poisoned condition" — but this could derail quickly. Now all characters carry manure in their bags, which is not what the game was supposed to be about.

For encouraging creativeness you can freely apply Advantage/Disadvantage or other advantageous mechanics temporarily for situational things. Like, a well-timed Light cantrip blinded the goblins, but this worked only in that scene. This is known as "making a ruling" and is favored by the 5e.

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    \$\begingroup\$ Very well built advice for a new DM. +many. 😊 \$\endgroup\$ Jul 13 at 12:18
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No, but yes

In short, this isn't going to work because your friend has their sense of scale all wrong.

The levels of energy involved in damaging elemental attacks are way beyond the very moderate levels where a bit of wool is going to help much. Ordinary cold weather clothing and ordinary flameproof attire exists in the world of D&D, but it just does the same things it does here, it doesn't defend against wizards calling up bolts of elemental energy and slamming them into you.

The attempt at a Faraday cage may be more feasible, but runs into the secondary issue that just because your player knows how to do that doesn't mean that the character does; a comparable example is how most players would be able to reinvent basic firearms if they had the resources of their character, but the commonly done thing when a player wants to attempt that (assuming the DM allows it at all) is that their character has to slowly develop the knowledge and do the research to figure out how to make it work, they can't just inherit all that real world knowledge from their player.

So, how does your friend's character get to create this interesting armour they're after?
Be an artificer. (See the supplement/optional rules in Tasha's Cauldron of Everything for details)

You're right that D&D lets you do almost anything, and it's already got a method for this. An artificer does exactly this kind of tinkering to create interesting items they can use to help on their adventures, with some magic thrown in to account for the point other answers have made about the difference between real fire and magical fire, for example.

The Artificer has an option at 6th level to give any suit of armour resistance against any one type of damage (aside from the purely physical damage types), and they can change it each time they take a long rest, if they chose. Now, it does only allow one resistance at a time, but if they take the Armorer subclass then their armor counts as 4 (or 5? I can't recall) different pieces, each of which can take a different magical effect. Normally you're only allowed to use the Resistant Armor infusion once at a time, but you're the DM and it sounds like you're looking for a balanced way to let your friend have what they want, since D&D is ultimately about having fun and yes is usually more fun than no I don't think it would be particularly unbalanced (though it's definitely powerful, so watch out when you design your boss encounters) to let your player learn/use the infusion several times so they can tinker with their armor and make it resist several elements at once.

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    \$\begingroup\$ I'd just like to mention that saying "yes but" or "yes and" instead of no is only half of the equation. The other half is not asking to do things that break the narrative. If you don't ask to jump to the moon I won't tell you that you can't. \$\endgroup\$
    – aslum
    Jul 14 at 18:50
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It works if and only if you let it work

You say it’s broken. Well, there’s your answer! You’re the DM, and it’s your right (and responsibility) to deny broken things. I get the feeling you want to know if it’s actually broken, and that’s a good thing to look into. But remember, you always have the right to say “no” on the spot—you don’t have to research the balance implications of every little thing players might come up with. Going with your gut feeling is fine.

It sounds like your player wants to treat the game like a lateral thinking puzzle, coming up with clever ideas to get around challenges. And that’s great, if that’s the kind of game you and your group want to have. As a new DM, if you haven’t yet, you should do some reading, particularly on making sure everyone is on the same page. Here’s a quick sample of resources (I’m sure others have more and better suggestions!):

…and if you let it work, treat it like magic anyway

Figure out what the armour would be worth as a magic item. (You ask about this in your question. I’m afraid I don’t have an answer for that.) Make him pay the normal costs for crafting such an item in his downtime. Maybe give it some sort of extra benefit, albeit a minor one.[1]

  • “Still works in antimagic” might be enough, if that’s something that comes up in your games. (A benefit that never comes up isn’t much of a benefit.)
  • It might end up being somewhat cheaper (but not by a huge margin).
  • It might tie into the story—this wacky inventor who makes magic-seeming things by mundane means has attracted attention.

It’s easy to justify this project being just as hard to do as magic. See, building this armour in a way that’s both effective and practical may well be impossible in the real world. But your average spellcaster does a half-dozen impossible things before lunch, so that’s no reason not to let it work.

But it will take research, and a lot of trial and error, to make it work. In other words, it takes time and money—two of the things that (by DMG rules) a character needs to make a magic item.

The third thing is spellcasting ability, but you can waive this if you like. You should still require something that represents character knowledge, though. You say the player is more knowledgeable about physics than you, but what about the character? Do they have any idea about the properties of electricity? They will probably have to do a lot of research and experimentation to even figure that out. Almost like they need to gain some experience in the area and develop their skills.

The revised downtime/crafting rules in Xanathar’s Guide to Everything may be helpful here. I don’t have the book, but I understand it removes the requirement to be a spellcaster. Instead, characters need to quest for specific materials they need, and they need proficiency in Arcana. You might substitute another proficiency for that, or you might say that science is just as “arcane” in a D&D world as magic is!


[1]: If you choose to let him do this, it’s because you agree that this is something fun that should be part of your game. So, you should reward the player’s creativity. Maybe being able to have his item is reward enough, but I can imagine him being disappointed if it’s no better than a magic item. So give it some sort of advantage… but it doesn’t have to be a big advantage!

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Quick Bullets

Since there are already in-depth answers:

  • Copper is denser than iron, so add the weight of an extra set of plate armor plus that of a wool rug. You are now overencumbered.
  • Likewise double the bulk of normal plate armor. Dexterity is nonexistent.
  • The face and limbs are still relatively exposed, if they plan on seeing, hearing, and moving. Those are still vulnerable.
  • Grounding a Faraday cage suit with a cable would immobilize the wearer around the tether, and give an enemy something to yank on

All in all, anyone who's been in a couple of tussles would know that attempting a life-and-death fight that way would be suicide

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If I was the DM, I'd let him build it but make him understand that if he wants to approach this from a physics standpoint then he gets all the drawbacks of physics as well.

First off, your copper outer layer only registers a 3 on the Mohs hardness scale. The iron and steel commonly used in weapons is much harder, which means a few weapon blows will tear the copper layer apart and compromise the entire suit.

With magical armor, resisting an acid-based attack makes the associated damage go away. What happens when a physical acid attack hits a flat copper surface? It splashes, everywhere. Sure, your armor's safe, but your exposed face isn't, nor are the teammates standing next to you. I'd rather take an acid splash to the chest than lose an eye. His outer layer isn't watertight since it's made of copper plates, so the acid would seep through the cracks and eat away the wool layer and your thermal protection.

The first law of thermodynamics is also going to work against the player here. The thermal energy from that fireball has to go somewhere. The player is essentially a ball of meat inside a slightly-insulated pot that's being held over an open flame. He might not take all the fire damage in one sudden burst, but it will roast him alive rather quickly. At a minimum, the metal will get so hot that it would severely burn the wearer wherever it touched his body.

This suit will do a poor job of protecting against electric attacks as well. Attempting to electrically ground yourself will force the energy of an incoming attack to flow through the armor and through the ground wire. Do you have any idea how much energy is in a lightning bolt? Lightning rods have to be thick to conduct away that much energy. Any suit that's physically wearable will be much too thin to be effective. At some metallurgically-weak point the armor will act like a fuse, shattering itself from the thermal stress of trying to conduct 1.21 GW of energy. With the circuit broken, your layers of armor, wool, and copper now act like a capacitor, which would protect you from small DC electrical signals but would do nothing against lightning.

In a game where casters can conjure up massive balls of energy out of nothing, the last thing you want is to dabble with physics. You want magical protection that can completely negate the incoming damage and send that fireball back into the nothingness that it came from. Your attackers see the laws of physics as merely suggestions that they can ignore or manipulate at will. Basing your defenses on physics isn't going to be very effective.

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