What ways are there to increase the HP of a shield?
I found Shield Boss', and I know enhancement bonuses will help as well.
Are there any other options like making the shield thicker?
It needs to be HP, as I am pushing damage into my shield and it bypasses hardness. 3rd-party content is welcome.
Different types of shields have different amounts of hp. Heavy steel shields (20 gp) and tower shields (30 gp) have the most, with 20 hp each.
Different materials can also affect hit points, though not very much. Adamantine items have the most, with ⅓ more than normal. A heavy adamantine shield has 26 hp.
Note that the rules only cover making light armor, medium armor, heavy armor, and weapons out of adamantine. A shield is not light, medium, or heavy armor, and so it is not covered by those. However, light and heavy shields can be used for a shield bash, and so are weapons, so you can make a light or heavy adamantine shield. The adamantine will cost 3,000 gp, and will overcome DR/adamantine on a shield bash, but it doesn’t provide any DR, or other defensive benefit, of its own. This also means you cannot use adamantine on shields which are unable to bash, such as bucklers or tower shields, so for the rest of this answer I’ll be focusing on a heavy steel or adamantine shield and not considering the tower shield option.
By the way, the rules aren’t super clear about what that ⅓ applies to. My assumption is that it only applies to the base hp of the item, because that makes sense to me—you’re just replacing steel with adamantine, so the increased hp should be relative to the hp of the steel, not relative to the steel plus other bonuses. That said, if the GM rules that some or all bonuses to hp are included in the calculation of the ⅓, you could get quite substantial bonuses from adamantine, up to +56 based on the options I’ve found and included in my calculations (a couple I have not because they are too costly to be considered or require specific choices of race and/or class that are not necessarily compatible with OP’s character).
As you noted, a shield boss can increase hp—the best benefit is a masterwork shield boss, for +15 hp, bringing a heavy steel shield to 35 hp and a heavy adamantine shield to 41 hp.
Each +1 of enhancement bonus adds 10 hp to the shield (see footnote 3 on “Table: Common Armor, Weapon, and Shield Hardness and Hit Points” in the damage objects rules), so a +5 heavy steel shield has 70 hp (also 20 hardness but that doesn’t matter for your purposes), while a +5 heavy adamantine shield has 76 (and hardness 30). With masterwork shield bosses, those increase to 85 hp and 91 hp, respectively.
Enhancement bonuses cost b²×1,000 gp, so a +5 bonus costs 25,000 gp.
Shields can be enhanced separately as weapons for when you bash with them. That means your +5 shield can also have a +5 shield bash—and both weapon and armor enhancement bonuses increase hp the same way. It’s not at all clear that these stack, and even if they do, weapon enhancements cost twice as much which is really questionable just from a cost-benefit ratio perspective.
If it works, it costs b²×2,000 gp, so a +5 bonus costs 50,000 gp.
For the following calculations, I haven’t included this, since it may not work and is rather inefficient even if it does.
An impervious weapon—which our heavy shield is (and must be for adamantine)—receives doubled hp from its enhancement bonus, meaning you could get another 50 hp out of it if you apply it to a +5 heavy shield, for a total of 135 hp, or 141 hp if adamantine. Since this is a weapon property, your shield needs to be a +1 weapon, which costs 2,000 gp, and then impervious is 3,000 gp. So it kinda costs 5,000 gp, assuming you weren’t otherwise enhancing your shield-as-a-weapon.
There is a question here, however: what enhancement bonus does impervious look at? The weapon enhancement? The highest enhancement among armor and weapon enhancement? All hp from any enhancement bonuses? Completely unclear. This matters a lot—if you need to get weapon enhancement, a +5 weapon costs 50,000 gp, rather than the 25,000 gp of a +5 shield, greatly increasing the cost of the benefit. On the other hand, if you can double both, in theory you could have a +5 shield with a +5 impervious shield bash and get 100 hp from the shield enhancement and another 100 hp from the bash enhancement.
For the rest of the answer, I’ve assumed that the hp from enhancement bonuses of shield and bash don’t stack, so you double only the highest one, which I’ve assumed is the +5 shield bonus.
A fortifying stone, among other things, adds 20 hp to an item that you attach it to. Note that the fortifying stone is destroyed if these hit points are lost (and they’re lost first like temporary hit points are, though they can be “healed” by fixing the object), but still, that gets up to 155 hp or 161 hp.
The last sentence of the description does refer to “any attached fortifying stones,” plural. RAW, multiple stones don’t stack, but if you can attach multiple, when one breaks, the next becomes functional, effectively replacing the hp with that of the new stone. Actually, arguably, you should constantly use the highest remaining hp of any stone on the shield, so they also kind of protect each other and they only start to break when they’re all depleted. That’s not quite as good as stacking—only one stone applies at a time, so you only get the one hardness bonus, and as for the hp, a big enough hit can destroy the current stone and damage the shield underneath before the next one comes online. Also, things that look at the shield’s hp—say adamantine, if it’s ruled to include bonus hp—will only see one stone’s benefit at a time. So rather than getting +6 hp/fortifying stone, it’s more like each fortifying stone gives +26 temporary hp.
Anyway, the answer you accepted with respect to multiple fortifying stones does suggest that much of the community is OK with allowing them to stack entirely. I’d probably allow the hp to stack just because adjudicating the thing where they cover for each other, unless you do too much damage in one blow, and then maybe you can repair some that survive, etc. etc., is just too much headache and not enough improvement for the game. I probably wouldn’t let the hardness stack, probably? Not that I’ve ever used sunder against a player’s equipment or ever intend to, so that might be moot.
Anyway, ask your GM. It’s a mess and the best solution here is to just discuss it and figure out what makes everyone happy.
The 3rd-level spell harden steel in the 3rd-party supplement Bloodforged by Dreamscarred Press¹ increases a metal weapon’s enhancement bonus by 2, gives it 10 temporary hit points on top of that, and also doubles the benefit of any special materials. If we’re talking about a +3 impervious heavy adamantine shield, that would be 40 hp from the +2 increased enhancement, 10 hp from the spell itself, and (probably) +7 hp for the improvement to adamantine. But for comparison purposes, I’m going to look at a +3 shield with harden armor vs. a +5 shield without, which means the 40 hp doesn’t count because the +5 shield has that too.
Unfortunately, harden steel only lasts 1 minute/level, which means you won’t be able to just pay someone to cast it. By the guidelines, having continuous harden steel on an item would cost 60,000 gp—contrast with the 16,000 gp to go from +3 to +5. That means 44,000 gp is getting you just 17 hp and 2 hardness. (For the record, 60,000 gp is so much that it still costs almost twice what it costs to raise a +8-equivalent shield to a +10-equivalent—even in that situation you’d be looking at 24,000 gp for the 17 hp and 2 hardness.)
The only way you’d even consider a continuous harden steel is if you have a powerful special material to double. Adamantine would be such a material for armor, perhaps, but not so much for weapons—at least, under the most likely meaning of the ⅓ rule. But if we had a favorable ruling, and adamantine increased all hp by ⅓, doubling that to ⅔ could be pretty significant, increasing the benefit to 67 hp over just increasing to +5 for real. But that is still not remotely worth 44,000 gp.
Realistically, harden steel only really makes sense if someone can already cast 3rd-level spells from a relevant list, is willing to use those slots on you, and you have decent enough scouting to know when to cast it. Then the cost is much lower, and can easily be done before you could have had +5 as a legitimate option anyway.
Anyway, the numbers here are so poor that I’m not going to include harden steel in my calculations in the following sections.
The matter manipulation power from Ultimate Psionics by Dreamscarred Press¹ can give an item “3 hit points per inch of thickness for every point of increased hardness,” which could be up to +5 hardness and thus +15 hp/in. Unfortunately, “per inch of thickness” isn’t very useful for items like shields, which don’t define their thickness. Realistically, a shield is less than an inch thick, but if we treat that as a minimum, this is +15 hp. Usefully, you can spend an hour manifesting matter manipulation to make it an instantaneous power, so that your shield becomes permanently stronger. So if you can find a 15th-level psion or wilder who knows this power, you only need them to do this for you once, and that brings us to 170 hp or 176 hp. Per the rules on spellcasting services, that costs a mere 1,200 gp. On the other hand, you need to find a 15th-level psion or wilder who knows this power...
In theory, if you found an unyielding legendary shield, it would have triple the hit points it would otherwise. Like adamantine, it’s unclear exactly which value is being tripled, but unlike adamantine, which is explicitly replacing just the steel, this is a powerful magical effect, that very well might apply to everything, or at least everything intrinsic to the shield (i.e. not the shield boss or fortifying stone but the rest of it). That makes it worth a great deal.
On the other hand, there is no way to buy a legendary item. You must either be a mythic character who takes the legendary item universal path ability, or else have an extremely generous GM who lets you find a suitable unyielding shield (unlike most legendary properties, unyielding is “persistent” and thus available to anyone using it).
Still, a conservative ruling on what the tripling applies to still results in a +5 unyielding impervious heavy adamantine shield having 458 hp. That’s a lot.
A bonded wizard adds 1 hp/level to their bonded item, which can be our heavy shield because it counts as a weapon. A kobold wizard can also add 1 hp/level to their bonded item, so a kobold bonded wizard adds +2 hp/level.
Arcane bond items also restore to full hp whenever a wizard prepares their spells.
This is not great. I doubt you were planning on being a kobold or a wizard, and +2 hp/level probably isn’t a good reason to change your mind. Technically, you can use someone else’s bonded item. I don’t know why that person would let you, but it is technically legal. I’m not going to assume you have someone who’ll let you do that, though, so you won’t see this benefit included in any of the following calculations.
A soul forger magus gets a benefit similar to that of a bonded wizard, increasing the bonded item’s hp by 1 hp/level. There is no kobold favored class bonus on this one, though, so it’s strictly inferior; just mentioning for completeness.
The blacksmith, by Drop Dead Studios as part of their Spheres of Might, can increase the hit points of items by their level, too. Unlike the bonded wizard or soul forger magus, this doesn’t have to be a bonded item—the blacksmith can just do it to every item they get their hands on. So if you have a blacksmith in the party, no reason to not have this benefit.
Still, I’m not going to assume that you have a blacksmith in the party.
With multiple fortifying stones, there is no real limit on how much hp you can effectively have, but your shield’s maximum hp at any given time appears to be 176 hp for a +5 impervious heavy adamantine shield with a masterwork shield boss and a fortifying stone, and having matter manipulation applied to it. If adamantine is allowed to increase all of the item’s hp by ⅓, including from bonuses, then it would be 226 hp. The cost, either way, would be 33,300 gp. This is with only one fortifying stone; as discussed, more fortifying stones don’t technically increase the shield’s max hp, though in practice they might as well.
In tabular form:
| Option | Hit Points (hp) | Cost (gp) | Efficiency (hp/gp) |
|---|---|---|---|
| Heavy steel shield | 20 hp | 20 gp | 100.0000% |
| Adamantine (likely rule) | 6 hp | 3,000 gp | 0.2000% |
| Mwk. shield boss | 15 hp | 80 gp | 18.7500% |
| +5 enhancement | 50 hp | 25,000 gp | 0.2000% |
| +5 bash enhancement | 50 hp | 50,000 gp | 0.1000% |
| Impervious | 50 hp | 5,000 gp | 1.0000% |
| Impervious (+5 bash) | 100 hp | 3,000 gp | 3.3333% |
| Fortifying stone | 20 hp | 1,000 gp | 2.0000% |
| +3 w/harden steel (vs. +5) | 17 hp | 44,000 gp | 0.0425% |
| Matter manipulation | 15 hp | 1,200 gp | 1.2500% |
| Adamantine (favorable ruling) | 56 hp | 3,000 gp | 1.8667% |
| +3 w/harden steel (") | 67 hp | 44,000 gp | 0.1523% |
| Unyielding | 282 hp | — | — |
Those are all the options I could find. There definitely could be more; unfortunately it’s very difficult to sift through things talking about “hit points,” so what I did was look for things that talked about hardness and checked to see if they also affected hp. There might be things that affect item hp without discussing hardness, in which case I’d have missed them. But as far as I can tell, this is it, and no, there is no option that is just “make the shield thicker.” If there were, that would certainly be doubly nice with matter manipulation. Note that my knowledge of third-party material is pretty much limited to whatever’s on d20pfsrd.com.
