Edge Protection: Armor enhancement for GURPS 4e and DFRPG

Edge Protection is a simple suggestion for a new GURPS armor stat which, together with DR, realistically simulates any level of armor rigidity vs flexibility and associated effects. It nicely handles some situations that current armor rules don’t, yet is no more complex than the existing flexible armor rules it replaces.


v1.0: Part of old article Gird Your Loins!.

v2.0: 2007.03.27

Taking the edge off

GURPS handles flexible armors like mail as follows: the wearer suffers one point of “blunt trauma” damage per full 10 points of damage (5 points if crushing) that doesn’t penetrate DR. In addition, some of these armors have a split DR score that offers full protection vs cutting and piercing damage, and reduced protection vs crushing and impaling damage. (See BS p. 379, and armor tables on BS p. 282-6.)

That makes for a workable if limited model. Flexibility becomes a simple binary switch (though the flexible armors with split DR could be seen as a third “very flexible” configuration). It doesn’t offer a good way to model armor like Frodo’s thin but unbreakable mithril shirt, which, as painfully demonstrated in The Fellowship of the Ring, will completely stop an edge from penetrating yet lets a huge wallop whack the wearer. But if DR is less than 10 (or 5 vs crushing), the GURPS “blunt trauma” effect can’t come into play anyway, making the “flexible” designation meaningless for almost all low-tech armors.

Oddities pop up, too. Even when DR is substantial enough to allow for the “blunt trauma” effect, a damage roll that goes just a little over DR and penetrates the armor can inflict less injury than a roll that’s fully blocked by flexible DR. On the lower end of the DR scale, armor with the split DR characteristic can infamously let an attacker deal more damage to the wearer by striking with the flat of his edged weapon, using this makeshift club to force the armor’s lower DR vs crushing.

There’s no huge problem with all of the above; it plays fine if you don’t look for the bugs. But for the interested, below is an alternative way to handle blunt trauma from armor deformation. It’s more realistic and flexible in what it models and avoids the above oddities, yet is easy and GURPS-like as well.

Edge Protection score

In addition to DR that completely negates the impact of a blow, armor can offer a lesser form of protection that allows the impact of a blow through, but prevents its edge or point from penetrating the armor (and flesh). I measure this property in points like DR, and call it Edge Protection (EP).

How it works

With two stats for armor, apply these two rules:

  1. Basic hits up to DR are absorbed, as always.
  2. Further basic hits up to EP do affect the target, but only as crushing damage.

In short, EP is a sort of extra DR that doesn’t stop basic hits, but does convert it to crushing damage. That’s it. Examining a bit more closely, you’ll notice the following:

  • If the blow is crushing, EP has no effect. Just subtract DR from basic hits.
  • If the blow is edged (cutting, impaling, or piercing), basic hits that exceed DR, but not EP, dent or otherwise deform the armor and bruise the wearer, but don’t penetrate the armor.
  • If the blow is edged, basic hits that exceed DR and EP actually do penetrate the armor. Those additional basic hits deliver their normal effect (e.g., take multipliers for cutting or impaling damage).

Example: You’re wearing chain mail with cloth underneath, for DR 2, EP 5. You’re attacked with an axe.

Your DR absorbs a blow of 2 or less damage. You’re not hurt.

A 4-point blow, after DR, leaves 2 basic hits. But those hits don’t penetrate EP 5; the mail is not cut. You take 2 points of crushing damage.

A 13-point blow, after DR, leaves 11 basic hits. EP limits the next 5 points to crushing damage; the mail isn’t cut yet. But the remaining 6 points break through the mail and cut you normally, for 9 damage after the cutting multiplier. You take 5 crushing + 9 cutting = total 14 points of damage.

If the weapon were a club instead of an axe, you’d just subtract 2 from damage for DR, and be done with it. EP would offer no special protection.

EP and flexible armor

These rules replace GURPS 3e‘s “roll of 5 or 6” rule, or 4e‘s rules for flexible armor and blunt trauma. There’s no special “flexible armor” designation under these rules; the combination of DR and EP models an armor’s unique resistance to both deformation and penetration.

EP and armor divisors

Unless you want to tweak things for special combinations of attack and armor types, apply armor divisors normally to both DR and EP, e.g., an armor divisor of (2) would halve both stats.

Benefits of EP

The benefit of EP to the armor wearer is obvious: edges hurt! A claymore swat to your mail-covered midsection may still knock the wind out of you, but that’s a heck of a lot better than getting chopped into haggis. The effect is particularly important where sensitive parts are concerned, most notably impaling and piercing attacks to the vitals. A little EP there can save you a lot of injury!

EP’s clear distinction between armor penetration and non-penetration can be useful to GMs, such as in determining whether a venomed weapon delivers its poison, or in implementing rules for accumulated armor damage and deterioration.

EP nicely simulates the ability of armor—even low-tech armor with modest DR—to keep its wearer in possession of his limbs, yet still get rudely battered by those axes and swords. And as shown below, EP allows for much greater customization of armor than DR alone does—up to and including magical armor that’s “impenetrable”, yet leaves the wearer anything but invulnerable.

Cost of natural EP

EP protects less than full DR. As natural armor, treat EP as a -60% limitation on the cost of DR, which becomes 2 cp per point of EP.

Setting armor DR and EP

DR represents resistance to any deformity at all; EP represents resistance to penetration but not deformity. The more flexible the armor, the more its protection will take the form of EP instead of DR. Tough, hard material, like a bronze chest plate, has high DR and low EP. Tough, flexible material, like mail armor, has low DR and high EP.

To rework existing stats, below are rules of thumb. Round values to the nearest integer (rounding up on 0.5). Keep in mind that a point of EP offers less protection than a point of full DR; reworked armor’s total DR+EP should at least equal listed GURPS DR, to maintain overall level of protection.

However, any armor can vary considerably from the suggestions below, especially in EP.

Very flexible armors

These would be the BS p. 283-4 armors given a “flexible” asterisk and a split DR score (higher score vs piercing and cutting, lower score vs others).

Set DR vs all attacks to the lower DR score. Then set EP equal to the higher DR plus half the lower—but halve EP vs impaling.

Example: Mail has DR 4/2. Use DR 2 vs all attacks, plus EP 5 (but EP 3 vs impaling).

Semi-flexible armors

These are armors with the “flexible” asterisk and a single DR score, like cloth and light leather.

Set DR to listed DR minus a quarter. Set EP equal to listed DR.

Rigid armors

These are armors without the “flexible” asterisk, like scale and plate.

Set DR to listed DR minus a fifth. Set EP to a third of listed DR.

Varying EP

You can vary EP a lot more than DR, without making armor too powerful or too weak. Take mail armor: no matter how high-tech and tough the metal, it’s a bit silly to imagine chain with a DR that repels heavy axes with no injury to the wearer. Yet it’s easy to imagine quality chain failing to split, even as the wearer gets battered by the blows. In practice, cheap materials might subtract 1 or none from DR, but halve EP; high-quality materials might add 1 or none to DR, but offer double or better EP.

A great example of very high-quality armor material is that Dwarven mithril mail, which saved Frodo from what would have been a fatal stab in the vitals. The mail’s extremely high EP allowed a big crushing blow to go through, but not the spear’s point itself.

Extreme cases

An Impenetrable Coat of Armor bequeathed by the gods might have no more DR than normal armor, but infinite EP. You can be bludgeoned to death wearing it—fairly easily so if it’s flexible with low DR—but it won’t be penetrated.

Make that a thin Shirt of Impenetrable Mono-silk, and you can have zero-DR armor that’s of no value in a fist fight, yet will stop a sword from running you through.

On the other end of things, a theoretical very hard, strong, but brittle armor, perhaps ceramic, would have high DR and no EP. Damage above DR simply breaks through the armor.

Sample Armor Table

Below are standard GURPS armor types, reworked with new DR and EP stats following the rules of thumb above.

armorGURPS DRNew DREPnotes
Lorica Segmentata542
Mail4/2*25DR 2, EP 3 vs impaling
Double Mail5/3*37DR 3, EP 4 vs impaling
Steel Corselet652
Heavy Steel Corselet762
Frag Vest5/2*26DR 2, EP 3 vs impaling
Tactical Vest12/5*515DR 5, EP 8 vs impaling
Tactical Suit20/10*1025DR 10, EP 13 vs impaling
Impenetrable Magic Armor(hypothetical)?infinite?DR depends on rigidity. EP limited only by definition of “impenetrable”.
Dwarven Magic Mail(hypothetical)412DR 4, EP 6 vs impaling
Dwarven Magic Plate(hypothetical)810DR 8, EP 5 vs impaling

Tweak those numbers as you like. Scale armor, for example, happens to get the worse of rounding on both DR and EP; boosting one of those by a point might be fair.

Also, it’s uncertain how plate inserts for modern flexible armor should be handled. The added plates presumably make the armor anything but flexible where impact is concerned; perhaps it’s best to add the plate DR to the lower of the original split DR score, and call that a single overall, non-flexible DR score with no EP.

Variations and tweaks

The above covers everything you need to play with EP. Below are options for the interested.

EP and attack types

EP can vary with attack type. The guidelines above already suggest halving EP vs impaling damage, for those flexible armors that GURPS designates as especially vulnerable to impaling. You may think of other worthy tweaks. As an extreme example, your Impenetrable Magic Armor’s infinite EP may drop to a low value (even zero!) when faced with the All-Penetrating Magic Sword.

Likewise, detail-oriented GMs will find EP a good way to model weapon sharpness. A blunt edge might double EP, and a very sharp edge halve it. This sort of tweak (essentially armor divisors that affect only EP) nicely modifies weapons’ armor-piercing ability without mucking up overall base damage or overplaying the role of DR.

EP and bullets

EP is definitely useful against large and huge piercing attacks, protecting the target from these weapons’ damage bonuses. EP will also save you from extra hurt vs small and regular piercing attacks to the vitals.

But EP leaves you no better off when regular piercing attacks hit non-vital targets—and it’ll actually hurt you more when small piercing attacks strike non-vitals! (EP turns those hits into regular crushing damage for a x1 multiplier, replacing the usual x0.5 multiplier for small piercing attacks.)

That’s not a flaw in the EP rules. GURPS rules that, compared to a blunt attack of a given force, a flesh-penetrating attack of the same force (i.e., same basic hits) can inflict the same damage (as with regular piercing) or even less damage (as with small piercing) than the non-penetrating equivalent. Whether this reasoning rings true or not, the above EP “oddity” is only following it to the letter.

It’s up to you whether that’s just as things should be, or a problem to be addressed. If the latter, you could rule that EP offers the lower of a crushing damage multiplier (x1) or the attack’s innate multiplier (x0.5 for small piercing vs non-vitals). If nothing else, that keeps EP from making the wearer worse off when small calibers attack.

Simplified EP

Using EP requires little extra work. But if you dislike even that, here’s a simpler version:

  • Subtract DR from basic hits, as always.
  • If remaining damage is less than or equal to EP, then damage is crushing (per rules above).
  • But if remaining damage exceeds EP, treat all of it as penetrating, with its normal damage multiplier; don’t bother adding the EP-blocked crushing damage to the EP-penetrating edged damage.

In other words, edged attacks that penetrate DR don’t deliver a realistic (but more complex) combination of crushing and edged damage; rather, once DR is exceeded, a cutting blow is all crushing or all cutting, and an impaling blow is all crushing or all impaling, depending on whether remaining basic hits also exceed EP.

It’s less realistic, but it is simpler!

Example: You have mail with DR 2, EP 5.

DR absorbs an axe blow of 2 or less damage; you’re not hurt.

A 4-point blow, after DR, leaves 2 basic hits, which don’t penetrate EP 5 so the mail is not cut. Take 2 points of crushing damage.

A 13-point blow, after DR, leaves 11 basic hits. Those 11 points exceed EP; the mail is penetrated and EP has no effect at all. Treat as a normal 11-point cutting attack, inflicting 16 damage after the x1.5 multiplier.

Complexified EP

Want the ultimate in armor realism? Use the full EP rules, with one addition:

For any and all basic hits absorbed by DR, apply 1/5 (round down) as blunt trauma damage, in addition to any damage suffered normally (i.e., by basic hits exceeding DR).

That’s for any armor, flexible or rigid or in-between. When armor “absorbs” a hit, it’s only spreading it out over a large area; a great big wallop, even spread over a large area, will still hurt! The net effect is that DR never completely dissipates basic hits (other than through the grace of rounding); it only lessens the basic hits a lot.

Example: You wear a heavy steel corselet with DR 6 (and EP 2, though that’s not relevant to this example).

Any time you’re hit for 5 or more points of damage, from any impact, apply all DR and EP rules normally . . . but when you’re finished, add 1 more point of blunt trauma, for the initial impact of the corselet slamming hard against you.

A thicker corselet with DR 12 offers even better protection—though 5 to 9 basic hits will still wallop you for 1 point of blunt trauma damage (even though DR was not exceeded), and 10 or more basic hits will inflict 2 points of blunt trauma damage (in addition to any hits that exceed DR). 

Final variant

With that said and done, there’s yet one more variation possible: use both the above simplified and complexified rules. Yes, they work together fine, resulting in something similar to the default EP rules in complexity, just a bit different in results.

EP and revised Toughness

How about this site’s revised Toughness? This isn’t 3e’s Toughness; it’s protection (generally from muscular or otherwise stout flesh) that lessens crushing blows a lot, slashes less so, or a stab to the vitals very little. It’s in some ways the opposite of EP. (Game terms: Toughness only subtracts from the basic hits of an impact, not the additional damage from edges, penetration and hit location.) Sounds like it’d be hard to juggle DR, EP, and this new Toughness, no?

Turns out it’s really very simple: A point of EP turns a point of edged damage into crushing, and a point of Toughness absorbs that point of crushing damage. Voila, a point of Toughness and a point of EP combine to have the same effect as a point of DR. Just treat the combination as DR. 

Example: You have Toughness 3, and put on DR 2, EP 4 armor. Toughness and EP combine to become DR 3 with EP 1 left over. Treat the total as DR 5, EP 1.

If you instead wear DR 1, EP 1 armor, Toughness and EP combine to become DR 1 with Toughness 2 left over. Add this DR to the armor’s DR: net DR 2, Toughness 2.

Let Toughness be a -40% limitation on the cost of DR, which makes it 3 cp per point. Thus, a point of Toughness and a point of EP add up to a point of DR in both cost and effect.

In practice, DR and EP alone are probably as much detail as many players will want. But I’ll note that with EP to stop edges from penetrating, Toughness to represent absorption of blunt force, and DR to combine the effects of both, you can model just about any armor effect with great realism.


  • alimantando

    I once heard, don’t know if its true, that in the beginning of firearms soldiers who could effort it (make that arristocrat officers) weared (what ist the past tense of wear?) silken shirts.
    A bullet did’t punch throug the silk, but dragged the shirt along on it path throug flesh, stopping after some inches. (Don’t try this with modern firearms :-).)
    The medic just had to pull the bullet out with your shirt an patch you up.

    I would say that counts as verry flexible armor.

    Maybe one could handel that as impaling damage over EP without breaking the armor. Don’t know.

    • tbone

      Hello! Interesting anecdote; I have no idea of the truth of it, but I heard the same comment recently on the SJ Games forums, too.

      I don’t know what sort of bullet might behave that way; only large and rounded shot, at relatively slow speed?

      Assuming it’s true: Hmm, if the bullet actually does penetrate flesh, I guess the silk shirt acts as only a little armor vs piercing weapons: DR 0, EP 1 (or whatever EP models the small degree to which the silk holds back the bullet’s penetration).

      The fact that the silk itself doesn’t get penetrated becomes an oddball special effect. I suppose it’d make sense to set some separate threshold (3 basic hits? 5? no idea…) at which the silk does get penetrated, if anyone cares. (Not that anyone should care much; intact silk pulled out of a bloody wound is pretty much as ruined as silk with a hole in it…)

      • Esteemed Visitor

        I don’t know what sort of bullet might behave that way; only large and rounded shot, at relatively slow speed?

        That sounds about right :-). A round lump of lead capable of flying about a tenth of a mile or something.

        I was thinking about this mono-silken shirt above. Suppose its strong enough to withstand a modern bullet. Does it protect at all? One could soak it in a coagulation agent to prevent bleeding.
        Or, of course, wear something with toughnes underneth. That would hopefully do the Trick.

        Stabbed with a knife of silk. How romantik.

      • tbone

        Huh. That silk is strong stuff! I wonder whether multiple layers of it might make really effective, all-around armor. And whether any armies (China?) ever did that. (At least for the elites that the armies could afford to spend big yuan on.)

  • tbone

    A friendly reader asks questions about the Edge Protection rule via email. I’ll respond here:

    1) Does the EP only limitation for natural DR replace traits such as Flexible and Tough Skin? If not, how does EP interact with these traits now that blunt trama has been replaced?

    EP would indeed replace the Flexible limitation, as it replaces the 4e flexible armor rules that the Flexible limitation calls upon. So instead of that limitation, just buy some or all armor with the -60% EP limitation. That’s a much bigger discount than Flexible’s -20%, but as pointed out in the article, 4e’s flexible armor has little game effect – almost no effect if DR is low. The EP limitation makes for a much bigger reduction in the armor’s effectiveness.

    (A side thought: if you buy 2/3 of your armor as DR, and 1/3 as EP, you’ll get the same net cost reduction as if you had applied Flexible’s -20% to all armor. So that purchasing scheme is the equivalent of Flexible, costwise.)

    Tough Skin in 4e works like (and includes) the Flexible limitation, with the extra limitation that the armor doesn’t protect against effects requiring a scratch (like poison) or skin contact (like electrical shock). It’s a -40% limitation, i.e., an extra -20% on top of Flexible’s -20%. So using EP rules, I would remove the Flexible limitation component from Tough Skin, and call the Tough Skin limitation a -20% limitation on the cost of armor; its only effects are the above non-protection vs scratches and skin contact effects.

    For any points of DR with the -60% EP limitation, adding the above modified Tough Skin means a net -80%.

    And despite what 4e says, why not allow regular, non-flexible DR to take Tough Skin, without the Flexibility component, as a -20% limitation? It may not be realistic, but if it’s conceivable, it could be bought as an oddball armor.

    Similarly, good realistic examples of “natural” EP are hard to think of. Natural EP suggests a hide that’s too negligibly thin to “absorb” a blow, but stubbornly resists cutting or penetration. Tough Skin doesn’t fit the EP concept well either: if the hide can’t be cut, how can it be scratched?

    But if you’re not concerned about the realism behind the armor, there’s nothing wrong with giving natural armor the EP limitation, the above -20% Tough Skin limitation, or both. Mix ‘n’ match, I say!

    2) How do energy attacks effect EP? Do you use adjusted DR and ignore EP, or have EP add to DR? In addition, how would corrosion attacks effect EP? In the normal rules, they reduce DR by 1 per 5 basic damage. Does it reduce both DR and EP, or is EP not affected and doesn’t help against the reduction?

    By the rules: If the energy attack has a damage multiplier, EP blocks the multiplier. No different from the workings for non-energy attacks. So a 10-point energy attack with a x2 damage mod, vs DR 2 and EP 4, will be reduced to 8 dam after DR. The next 4 points will inflict 4 points of crushing wallop. The remaining 4 points of damage penetrate and are doubled to 8 damage. Net: 12 damage (4 crushing, 8 energy). EDIT 09.04.30: I edited these numbers, which appear to have been screwy.

    You could adjust EP vs energy attacks up or down for any specific armor; it may make sense for some concepts. Buy DR with the EP limitation and an “only vs energy” or “only vs non-energy” limitation.

    As for corrosion: I hadn’t thought about that. Good question. Off the top of my head, I would say “Treat EP like DR here: a point of corrosion loss will remove a point of DR or a point of EP – the GM decides which, or make up some rule for which goes first.”

    But that’s not too good a solution, maybe. Take a low-DR, high-EP “unbreakable” flexible armor: using the above rule, DR might disappear quickly, while lots of EP remains even after many, many attacks. What exactly is the state of that armor? The acid wore it down to a super-flexible paper-thinness, yet it’s still whole and resists penetration?

    Should high EP – “unbreakability” – necessarily mean high resistance to corrosion? If not, then corrosion should affect DR only, and EP could be removed in the same proportion (i.e., when you lose half DR to corrosion, you lose half EP; when you lose all DR to corrosion, you lose all EP, even if it was magically infinite).

    I don’t know what sounds “right” for DR, EP and corrosion. What do you think?

  • Devotee of Reason

    Regarding the difficulty with ceramic inserts for bullet-proof vests.

    I really don’t see the need to complicate things by having them lower or remove the EP bonus. If the bullet *does* break through the ceramic plate, the kevlar will still slow it down and distribute the force. The stuff in front of the ceramic may have less room to deform , but the stuff behind the ceramic will behave surely behave as normal.

    • tbone

      I guess I was imagining Kevlar on top, ceramic plates beneath. If that’s reversed, then keeping EP active, as you suggest, seems sensible.

      And if the plates are sandwiched between equal layers of Kevlar? Then I would halve the listed EP (the EP of the Kevlar half above the plates has no effect; the EP of the Kevlar half below the plates is able to act normally).

      I myself don’t know which of these best models the real armor!

  • Hal

    One of the things that bugs me about the current rules for flexible armor is this:

    Why is it, that Chain itself loses 66% effectiveness against blunt weapons by virtue of being flexible armor, while other flexible armor types do not?

    I can almost hear people stop a moment and think “66%? GURPS has it that it loses 50%, not 66%”

    Proof of my point is thus:

    DR of chain by itself is 3/1
    DR of Leather by itself is 1
    DR of Leather backed Chain is 4/2

    Note that leather adds to both Cutting DR and Blunt DR by +1 point, while chain by itself is reduced by 2 levels out of 3 – hence the statement that chain’s DR is reduced by 66%.

    My question becomes one of “Why does one type of flexible armor lose 66% effectiveness against damage while all other flexible armors do not?”

    • tbone

      Hi Hal. I saw the similar comment on the SJG forum, too. Re the issue: I may be missing part of what you’re pointing out. If it’s only the question “Why does Leather not lose any DR vs Blunt, while Chain loses 2/3 DR?”, I suppose two answers could be given that would mesh with officialdom:

      1) Both are “flexible”, but they’re still different materials with different properties. Sharing the same “flexible” designation doesn’t mean they need to share the same split DR properties.

      2) Leather actually should lose 2/3 DR like Chain, but with only DR 1 to begin with, that just gets rounded back up to 1. The DR stat is too low to support the difference.

      Of course, I don’t know that either of those actually is the official thinking!

      Either way, my beef remains a little different: the split DR is simply buggy in its effects (i.e., letting you boost “penetration” by using the sword flat). Not game-wrecking, by any means, just odd.

      Off-hand, I don’t see game problems with any armors that use a higher DR for blunt than for edged. It may or may not be a good simulation of any specific armor, but I don’t foresee a problem with oddball game effects.

      But armor with lower DR for blunt generates the above strange outcome, and what’s more, I can’t imagine an armor type that would reasonably act that way, including Chain.

      Or am I missing a situation where lower DR for blunt does make sense? Anyone?

  • Ogo

    Hello! It appears this conversation is a little stale at this point, but I’ve enjoyed reading it nontheless!

    I do have a question however. It appears that the EP concept, as you’ve worked it out, has just made high-tech and ultra-tech armors much less effective against bullets. If EP converts pi damage to cr after DR is subtracted, what’s the difference? Your nice DR 20 suit is now DR 10.

    Am I missing something here, or is that the point?

    • tbone

      Hi! I think your question is answered toward the end of the article, under “EP and bullets”. In short form:

      GURPS says impacts hurt you, and hurt you even more when sharp edges pierce flesh. That’s sensible, and it’s handled cutting and impaling weapons right from the game’s beginnings.

      EP is a great way to model protection against those edges: With EP, the edges don’t pierce, so the extra hurt isn’t there.

      Then bullets came along, and GURPS said that the impact from pi bullets hurts you… but doesn’t hurt you any more by piercing flesh.

      So EP fails to have any effect there, but that’s not EP’s fault. The game’s pi bullets just don’t follow the sensible lead set by cutting and impaling impacts.

      I’ve always thought bullet rules should sensibly work like cutting or impaling: some basic impact, plus a damage modifier greater than 1 for piercing flesh. (That is the case for bullets hitting the vitals – and as expected, EP works great to protect that location against bullets.)

      But assuming no changes to bullet rules, then for non-vitals targets, you have to implement some patch to overcome that quirk and make bullets play nicely with EP. : (

      • Ogo

        I hear you, on the question of bullet damage. I rationalize it by saying that the “modifiers”, if they existed, would basically even out. As in, the damage as listed represents the energy of the bullet hitting you. Then there would be a big divisor representing how little mass a bullet has, then a big multiplier representing the deep wound. Call it “high velocity tiny impaling” and be done with it 🙂

        Regarding bullets, ballistic armor and EP, you may need to come up with a fourth category for it. I don’t know if the “very flexible” bucket is right because I am not sure kevlar is just a really good version of chainmail or a different substance entirely. 4/2* sure looks different from 35/5* or whatever!

        You could also have both DR and EP count as DR vs. bullets but that would inflate the value of ballistic armor rather than deflate it.

        Another idea I’m toying with is saying that imp damage always halves EP, instead of setting the EP of certain armors lower vs imp

        • tbone

          Let me add: I’m not saying there can’t be a sensible case in which EP actually increases the damage you take. Imagine, say, some strange form of projectile that’s thin and needle-like, but with high mass (maybe long and super-dense)? When it hits a hard surface, it packs a real wallop. But when it hits flesh, it passes through the flesh, dissipating very little energy as damage, and leaving a very tiny wound channel.

          Now add some armor that’s super-thin and extremely flexible, but just won’t let that super-needle penetrate. Instead of the projectile whizzing through flesh like a surgeon’s needle, it slams against the armor, dissipating loads of energy into the underlying flesh as a massive bruise.

          Okay, maybe “sensible” isn’t the word; both the projectile, and the low-DR, high-EP armor able to resist penetration by such a massive and sharp “needle”, don’t sound like something you could pick up at the arms dealer’s. But under that semi-possible concept, anyway, suffering more damage because of EP is simply an interesting consequence of the factors involved. It’s one way of reasoning that the strange bullet/EP interaction is just fine as it is.

          BUT, it all doesn’t sound right to me as a model for real bullets – especially since these, even small ones, can leave good-sized messy wound channels, not needle-like tracks. That’s why I’d prefer a damage mod >1 for all bullets…

          Now, putting that aside and moving on to some solution for actual game play… Maybe something like this:

          For any attack with damage mod > 1, EP reduces damage mod to 1. That’s per EP rules as written.

          For any attack with damage mod <=1, EP halves damage after applying the mod. So it turns normal pi (x1 dam) into x1/2 dam, and turns pi- (x1/2 dam) into x1/4 dam. That might work as a way of handling bullets etc. Heck, one could even go further, and revise EP for all situations as follows:

          EP simply halves damage. For post-DR dam up to the amount of EP, apply all modifiers normally (for cut/pi/imp, for target location, etc.), and then halve that dam.

          That lets EP provide some protection vs impales and pi+, vs pi and pi-, and even vs crushing attacks – essentially, it would offer some “padding” effect in addition to simple penetration-resistance. On the other hand, the change decreases EP’s value in high dam-mod cases – for example, the dam mod for imp vs vitals drops from x3 down to x1.5, not down to x1. It all balances out to some degree. EP would retain the special effect of not allowing penetration (so that impale to the vitals would still be a massive bruise, without piercing armor and cutting flesh and introducing poison etc.).

          Hm. What do you think?

          • Ogo

            Short answer: I dunno!

            Let’s leave aside the bullet damage issue — the amount of brainpower visited on that subject by the gun nuts on the GURPS forums is frightening enough to believe it’s generally OK.

            1. If DR represents “stopping all force and objects from getting through” and EP represents, “letting force, but not the damaging object itself through,” it’s a matter of determining a) what those numbers are for a given armor material, and b) how each damage type plays with those numbers. And I don’t know what realistic values for a) and b) should be. And, c) it should be relatively simple to use in play.

            2. Without any evidence, I’m instinctively in favor of the “all of nothing” tweak for EP. If a weapon breaks through the “stopping all force and objects” hard part, the “stops objects but not force” soft part wouldn’t do much either, would it? The odd detail of a stab-through-mail producing a small crushing (damage within EP) and a small impaling (damage above EP) wound doesn’t seem right either.

            3. The DR and EP concept you’ve laid out here looks good, it’s just bullets and ballistic armor that don’t fit very well. How well do bullets punch through mail and plate? How well does ballistic armor protect against bats, or swords?

            There might be three possible numbers for a given piece of armor:

            * How well it keeps its shape and rigidity; raw material strength (DR, sort of)
            * How difiicult it is to break through to reach the wearer directly (EP)
            * How well it disperses or absorbs force (the quality inherent to ballistic armors, also represented by DR).

            This last quality could be represented with a Damage Reduction number, but assessing realism is next to impossible, and retaining playability is quickly going out the window…

            • tbone

              On the three numbered items:

              (1) Sounds fine. Though, like you, I don’t know what the “right” numbers should be for any given armor. (Which is fine with me; just put some number in place, and should data ever come up to suggest a change, then change away!)

              (2) I’ll stick to my guns on this one: If an attack expends some energy breaking chainmail, then what penetrates has less energy remaining. I think it becomes trickier when you envision hand-held stabs, as there’s the matter of the attacker continuing or even renewing his “push” once the blade pierces armor. But for simplicity, just to mentally play with what’s going on, imagine a thrown spear. If the spear barely has enough energy to break and actually penetrate chainmail, then what just manages to penetrate will logically cause little piercing of flesh.

              That said, the above doesn’t mean that EP needs to absorb lots of energy; just set EP low vs the damage type in question, and the bit of edged damage converted to crushing will be low. Or, just go ahead and use “all or nothing”, per your preference; while I think it’s a small drop in simulation realism, it’s a nice simplification, and in most cases won’t yield results very different from the base rule.

              (3) Same questions here. Again, all I can do is guess.


              As for those three possible types of armor:

              Yes, that sounds reasonable. In fact – and I may have mentioned this somewhere on the site – in the many discussions of flexible armor and/or EP here or elsewhere online, I’ve been surprised that people never mention one of the things that the current flexible armor rules do offer, that EP doesn’t: A damage divisor. That’s essentially what the current flexible armor rule offers.

              I think a damage divisor as an armor effect is in theory a fine thing! I don’t think the current flex armor rules handle it well, for reasons outlined in the article. But the general idea could be reworked into something sound.

              Awesomely detailed armor rules could offer three types of protection, with an attack needing to penetrate them in order:

              1) Full absorption of impact (DR). At this point, the armor is not broken or deformed at all. (Same as the first armor quality you suggest.)

              2) Dispersal and partial absorption of impact (handled as Damage Reduction). At this point, the armor is deformed somewhat. (Matches the 3rd armor quality you suggest?)

              3) Prevention of penetration only, but not impact (EP). At this point, the armor is not broken but is seriously deformed, providing no appreciable padding or spreading of the impact. (Same as the 2nd armor quality you suggest.)

              Mix up those three, and armors would get pretty darned realistic, IMO. In fact, while I think EP is perfect for extreme cases like thin impenetrable magic/tech armor, real armor might hew closer to DR + Dam Reduction than to DR + EP. For simplicity, EP could even be replaced entirely with Dam Resist, per my earlier comment.

              Using all three of the above armor qualities might play too fussily. Using only two is pretty simple and yields better results than the current flex armor rules, IMO.

  • yojimbeau

    Got a puzzler for you. How would you apply EP rules to the following:

    Thick Skin*: Piercing 33*, Cutting 23*, Burning & Crushing 21*, Other 11*, and Skull +20. This is a package of enhancements for an ultratech TL10 combat bioroid. I can handle simple armour conversions (but I use 1/2 EP and only apply the Cutting wound mod if basic damage >DR+2xEP. Also seems logical to count DR+EP versus corrosion and burning ie no blunt trauma).

    • tbone

      That’s some complex armor! Application of EP would of course depend on the effect wanted. Is DR so high (Piercing 33*) because the armor is really supposed to offer incredible protection even vs very high damage (in which case I’d use high DR and modest EP), or is it so high just in the attempt to simulate incredible penetration resistance (in which case much lower DR but great EP might be good)?

      Well, not knowing that, and just to see what happens, we could apply the suggested rule of thumb for very flexible armor… but results aren’t totally clear, since this armor has multiple split DR. Hmm, how about we use base DR 21 (taken from “Crushing”) as the “lower DR score”, and then for each of the other damage types, use its original DR + (half of 21 = 10) to get EP. So: Piercing = DR 21, EP 43; and Cutting = DR 21, EP 33. Crushing, of course, is just DR 21. (As for the “Other” damage type: …I don’t know, would EP be relevant?)

      So there are some starter numbers, but those could be adjusted wildly, as much as desired.

      Re cost: EP is a -60% limitation on cost of DR. That already includes what 4e calls a -20% limitation for Flexible. But, per discussion in the comments, add another -20% if the armor also has the demerits discussed for 4e’s Tough Skin, which (as one example) lets any scratch deliver poison even if armor resists damage/penetration. So, EP becomes a net -80% if it can’t stop secondary effects like poisons; and even the underlying normal DR can optionally take that -20% too, if it also can’t stop secondary effects.

      Now, a remaining problem: How to price EP that differs for Cutting, Piercing, etc.? Or how to do so for DR, for that matter? Is the cost of split DR already covered in 4e??

      Finally, as for the skull: That’s be just plain DR, no EP, bought for a small body location; does that sound right?

  • Gato

    What about knives for example. The damage you deal with a knife is almost exclusively done by the edge and has practically no impact. Nevertheless, if the defender wears an armor with high EP and low DR then such attack might leave a bruise as if hit by a heavy weapon (clearly not the case). I just dont picture the scene of someone been bludgeoned to death by an atacker wielding a knife !

    I only know the basics of GURPS but im actually designing my own rpg system and was having some trouble trying to sort out this very problem of cutting edges and impact of blows.

    P.D.: My mail is sachiel03ar@hotmail.com

    P.D.2: I know… my english sucks.

    • tbone

      It’s a fine question. The answer, for the purpose of these rules, is pretty simple: I’m only working with the assumption that basic hits do measure impact, for knives or fists or maces or any hand weapon. If there’s a problem with knives delivering too much sheer impact in the game, then that’s a problem not for EP rules alone, but for any GURPS rules dealing with that impact (effects of knives vs DR, knockback from knife attacks, effects of knife attacks on other weapons, etc.).

      I don’t know that knives actually do deliver far too much impact in the game. After all, a fist can deliver tremendous (even deadly) impact; should a large knife really deliver much less impact? It is a hard metal object, and to some degree, the mass and power of the fist/arm also add to its impact.

      If, however, you feel that impact should be lower, then I would rework the rules to reflect that (whether or not EP rules are being used – and, as you suggest, whether we’re even talking about GURPS or about your own system). In particular, I think impact from a thrust knife should be on par with a punch (even able to pierce armor), so impact shouldn’t be too low. But I also think that swing impact would rely more on a weapon’s own mass, with less added effect from the fist/arm. Especially for a small knife, impact should perhaps be quite low (as you suggest), giving a razor or other small knife little ability to bludgeon through armor, and low damage against flesh if simply used to “hack” like an axe or other large weapon. In place of high impact, I think such a weapon should have a good ability to “slash” – that is, draw along the target for an attack that delivers low basic hits, but a higher damage multiplier vs flesh than normal cutting.

      GURPS doesn’t make that distinction; maybe you’re planning to do so in your own system?

      • Gato

        Hi, I read and re read your reply several times and found it very interesting, I really enjoy to know about someone who knows what he’s talking about.

        I actually solved my problem with cutting and impact damage of cutting weapons for my system, im willing to discuss it anytime if you like. Thanks for your help !

        • tbone

          In my own slowly-merging homebrew system, impact and related topics are precisely what I’m fussing over at present. I’d be happy to hear details of what you’ve done and share ideas.

  • Ned

    A few questions about this.

    1.Outside of Basic Set, Scale Armor receives a -1DR vs Crushing, and in the Armor Design System from Pyramid 3/52 Fabric construction type, so Cloth, gets a -1 vs Impaling, how would you treat those armor types under this system?

    2.How would you combine this approach with Armor As Dice? Say I have the Corselet(5DR 2EP), I roll 3d-1 cut damage against it. How is this handled? So 5DR gets rid of 1d+1 dice. so we are down to 1d+2 after that. What does the 2EP actually do? I mean do I just deal a flat 2 crushing damage and subtract 2 from my remaining 1d+2 damage, and then move on to rolling 1d Cut which actually penetrated the armor?


    Do I actually roll 1d-2 for the Crushing damage? I ask because “technically” that 2EP means 2 damage, but 2 damage, means 1d-2, which could mean 2 damage but it could also mean as little as 0 or as much as 4.

    So how would you handle that?

    • tbone

      Hi there!

      1. If Scale Armor DR is reduced by 1 vs crushing under an optional armor system, then I’d simply reduce DR by 1, vs any impact. A core part of these EP rules is “impact is impact”, whether the weapon is blunt or not. So if Scale Armor offers poor protection vs impact (as indicated by “-1 vs crushing”), then so be it. That’s lower DR all around.

      But if said Pyramid rule is intended to otherwise leave penetration vs edges untouched, then I’d make up for that -1 DR with an extra point (or more) of EP.

      (Side note: Poor Scale armor. It’s such a dog in DFRPG, stuck with horrible weight for very little cost saving. Nobody wants it, and I feel sorry for it. Edit 2023-09-16: I should specify that I mean Heavy Scale. Regular Scale has its niche between Mail and Segmented Plate. Heavy Scale is just a dog between Heavy Mail and Heavy Segmented Plate.)

      And Cloth? If the armor is a base DR 1 but you reduce that by 1 vs impaling… I guess the Pyramid rule intends that basic DR 1 cloth offers no protection at all vs impaling? You could call that DR 0 EP 0 vs impaling… but taking into account unusually thick cloth armor (which would still retain DR, right?), I think I’d just go with “halve EP vs impaling” to model the concept “this armor is easily penetrated by impaling”.

      Whether to then also reduce DR… Without delving into real-world info on impaling penetration vs cloth armor, I think I’d just keep the rules’ “-1 DR vs impaling”. So -1 DR, half EP. (That’s in line with the general approach that these EP rules take toward “Attack Type X vs. Armor Type Y”: Don’t muck with DR too much, as halvings, doublings, etc. of DR hugely affect the armor’s worth (and combat balance). Do muck freely with EP to get desired effects!)

      Of course, with EP only 1 point, mucking with it a lot still doesn’t do much in this case. Taking cloth armor with DR 1, EP 1, we get DR 0, EP 1 vs impaling (rounding up the halved EP, so we still have something). Does that sound reasonable?

      1. Armor as dice:

      I’m going to punt on that one for now (is that the expression?). I’m loosely familiar with the idea, but haven’t perused it throughly and haven’t played it at all. I’ll need to reacquaint myself.

      Actually, this whole article needs an update, to make some new observations that have come up, to better address DFRPG, and to look at integration with more armor rules variants, like armor as dice and the Pyramid article you reference.

      Speaking of which: If you or any reader know of other relevant armor-related articles in Pyramid, or variant armor rules squirreled away elsewhere in GURPS, please let me know. It’d be good to tackle all at once.

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