The other main solution is reductive armour. Unfortunately, most implementations of reductive armour are very clunky, and require extensive battleboarding ("So a single is six points of damage, a double is twelve, and a bastard double is nine, but then my armour takes off from one to five of those?"). So I've spent a while playing with how to get a system that satisfies both being easy to use and being reductive.
Changes since the last major version
To my mind, the biggest issues with ablative armour are that it stops being useful partway through a fight, and that it doesn't also drive weapon choices. With ablative armour, the number one survivable choice is sword and board, as we've seen at Maelstrom, which looks a bit rubbish if you're wearing full plate. The problem with reductive armour, by contrast, is complexity - you need either to be constantly adjusting damage grades in your head, or to battleboard, neither of which are optimal.
So, what do I want to see a larp armour system do?
There's a few bits of the rules that basically any system which is wanting to achieve something like this will need to have. Obvious parts include: two-handed weapons doing inherently more damage than one-handed. Most important, perhaps, is "no through damage", as that makes it possible to build reductive armour in what is perhaps the easiest way.
So, how does this all work? It's shamelessly based partially on Odyssey, with bits borrowed from the Empire playtest at Mael1 2012, and partially on some other drafts of this sort of system I've put together before.
Body hits
Characters have four base hits. Very frail ones might have three, exceptionally strong ones five.
Armour will give you a multiplier, from 1 (no armour) to 4 (full plate). This is used to scale your body hits in combat. If you have the standard four body hits, and are wearing a tough plated-leather jerkin, you have a multiplier of 1.5. This means you can then take six hits in combat. Fractional body hits will round up - if you only had three, and wore the same armour, you would then count as having five.
Healing is thus applied to your hits 'before' armour. If you are fed a potion that heals two hits, this means it will heal twice your current multiplier's worth of hits. In the above case, you would regain up to three hits. There is no armour repair mechanic, and no way to destroy armour.
Furthermore, if you remove armour while partially injured, discard any partial hits. If you are wearing full rigid armour, and thus on sixteen hits, and take six singles, you can then take ten more singles. If you then remove the full plate, putting your multipiler down to one, you will have lost one of your four hits, as 1.5 hits (the actual number you've lost) rounds down to just 1. This means that you will never be incapacitated by removing your armour.
Armour categories
There are three categories of armour: light, flexible, and rigid. To go with this, there are two possible levels of coverage: torso and full.
Torso coverage requires a cuirass + gorget, a vest-sized mail shirt, or equivalents in lighter options. Wearing something like just a breastplate over a mail shirt would also count as torso plate. Full coverage requires at least half of every limb to also be protected by that level of armour, and the rest ideally protected by at least a lesser level (so full mail could be physrepped by a half-sleeved hauberk, with leather greaves and vambraces). All resistances from torso armour only apply for attacks which strike the head or torso. Resistances from full armour apply to any attack
Light armour
Light armour consists of padded and/or leather defenses. It's the least encumbering, but provides the least benefit. Valid physreps for light armour include leather garments with reinforcements, padded or quilted garments, thick leather defenses, leather lamellar, and so on.
Torso light armour multiplies your hits by 1.5
Full light armour multiplies your hits by 2, and downgrades cleave to just one point of damage, but still disabling the struck limb.
Flexible armour
Flexible armour is a category including all forms of flexible metallic armour. Mail armour, scale armour, lorica segmentata, metal lamellar, and other such armours all fall into this category. To be a valid physrep, the armour must be at least partially made of some form of metal - stringmail and plastic mail don't count, while aluminium/neoprene mail, ringmesh/butcher's mail, aluminium mail, butcher's scale, and the like all do count.
Flexible armour must be worn over a thick tunic, or a physrep of a gambeson or padded jack. This doesn't have to be actually effective, but must at least look quilted or padded.
Torso flexible armour multiplies your hits by 2, and downgrades impale to triple.
Full flexible armour multipiles your hits by 3, downgrades impale to triple, and downgrades cleave to single.
Rigid armour
Rigid armour covers plate, brigandines, and other such forms of rigid, sturdy, and extremely protective body defense. Valid physreps for this category are anything either made of or clearly appearing to be made of metal, from full steel plate, through aluminium plate, to norton style plastic plate. Rigidly splinted metal armours also count, but the splints shouldn't have independent movement. Full coverage of rigid armour is a bit more stringent than the other categories - at least 2/3rds of the limb must be armoured with a valid rigid armour physrep, or all of it if parts are less well protected (needs rephrasing). As an example, this would mean that cuirass, vambraces, and greaves only counted for torso rigid armour. Adding cuisses and pauldrons would count for full, as would adding a mail hauberk.
Rigid armour must be worn over a physrep of a gambeson, padded jack, or arming doublet. This doesn't have to be extensively padded, but must look like it's constructed to be a baselayer for armour.
Torso rigid armour multiplies your hits by 3, and downgrades impale to triple.
Full rigid armour multiplies your hits by 4, and downgrades cleave, crush, and impale to single.
Stealth armour
Armour may be worn under a tabard or surcoat at no penalty. Wearing armour fully concealed, however, requires making certain compromises in the suit. Concealed armour therefore doesn't have the resistances that visible armour does, but does give the extra hits.
Mixing armour types
Clearly, adding a breastplate to your mail will improve your defenses. However, wearing leathers under your full plate won't really do anything for you at all. Therefore:
When wearing multiple suits of armour, you take the best multiplier from any suit you are wearing for your overall multiplier. Your resistances are the best of those granted by the armour you're wearing on that area.
As an example, if you wear full leather armour and a mail shirt on your torso, you will have a multiplier of 2. You will also treat any arrows which hit you in the torso or head as calling TRIPLE instead of IMPALE.
Calls
Skill trees
This is just a sketch of how skills would work. Trees would generally give per-combat uses of special calls. Weapon trees might include:
Fencer: Use of rapiers and smallswords. Per combat calls of MORTAL, at higher levels the occasional use of DOUBLE.
Shivver: Use of daggers and the like. Per combat calls of MORTAL, at higher levels the occasional use of TRIPLE and STRIKEDOWN (representing grappling).
Knight: Use of bastardswords, short pole weapons, and the like. Natural DOUBLEs, per combat calls of CRUSH and TRIPLE and STRIKEDOWN, also covers arming swords.
Skirmisher: Use of single handed weapons with shields. Natural SINGLEs, per combat uses of CLEAVE or CRUSH as appropriate
Archer: Use of bows. Calls of IMPALE. Tree also branches out and gives some of the stuff from Skirmisher and Shivver, probably.
Conscript: Use of long polearms. Some strikedowns, the occasional TRIPLE at higher levels.
Due to the lack of a THROUGH call, your armour essentially multiplies the number of hits you can take - light armour doubles it, full plate triples it, and so on. This is the same overall effect as making you only take half as much or a third as much damage per blow, but much easier to count.
The requirement for torso coverage instead of partial coverage means that partially armoured people look a lot more visibly armoured, which is nice - wearing a cuirass and tassets as partial armour looks a lot better than wearing some random bits of greaves and vambraces. Similarly, the baselayers for flexible and rigid armour help that look more visually interesting as armour, not just a few decorative pieces strapped on over normal clothing.
Visible armour and defined armour effects means that people can intelligently use their limited resource calls. Archers can prioritise targets in lighter armours. Fighters with uses of CRUSH or CLEAVE can prioritise these attacks against foes who will be more affected.
Crush appears to be strictly better than Cleave. Intentional? --MorkaisChosen
As a TODO for myself, I think I'm going to tweak the number of base hits a bit (to four), and make all of the armours actually multiplicative. On top of that, will be defining how removing armour while partially injured works, and generally adjusting it all slightly to make it plug-in compatible with Tea/EncounterLARP or similar. --Tea
A note WRT the gambeson/baselayer fact, given LARPers tend to wear the armour all day, heavy base layers are not practical. On days that would be considered chilly I was unable to wear gambeson, chain with kimono over the top. --Drac
A different ablative armour principal is the York one - damage on armour counts as single. (From memory your average character was around 3-5 hits per location and 1-5 points of armour, triple seemed roughly equivalent to melee 5 in terms of prevalence). They have through (which obviously becomes much more powerful) and Cleave which did full damage to armour. --Drac
I'm undecided on CLEAVE. The current version makes it slightly better than CRUSH for mowing down peasants, which I like. I don't have any issues with it just being strictly worse, though - swords are already common enough.
The interaction of the current CLEAVE with FLA is my biggest concern, though. On the one hand, it's nice as it means that wearing full light with partial plate is actually a useful choice - adding the extra armour does in fact give you a game benefit. On the other hand, it's reduction, which I dislike. Opinions? The options are basically a) drop cleave back to single, b) drop the resist from fla, c) keep this version --Tea
It's potentially advantageous to take armour off- if you have 4x-multiplier plate on, get taken down to one hit, and then take your armour off, you're then left on one hit. If you put the armour back on, you'd then be on... 4 again? It also makes healing a bit more efficient, but I think "you get a bit more out of healing people if they take the time to take their armour off so you have better access" is a kinda cool emergent feature. (Things like 1 hit left in x4: 1 point of healing takes you to 5 left. Take the armour off, 1pt takes you to 2, put it on again, 8 hits left.)