About a year ago now I started looking into what exactly Material did for the armor I was wearing. This was in an attempt to build a better understanding of my equipment to make up for the fact that I can't fucking aim. I found a few things. One, each material has a different cost to repair it in terms of the maximum durability removed. Two, each material has a different damage multiplier that's applied to the 'Armor Damage' stat found on the bullet hitting you. These multipliers are as follows:
Very Good Repair
Combined Materials: 0.5
Armored Steel: 0.7
Very Good Repair
Very Bad Repair
What this means is that each piece of body armor you put on is drastically different than what you probably think it is as far as durability goes. Most people tend to ignore things like the Ballistic Applique for the Caiman or the SLAAP up armor plate for the FAST-MT line. I think this is a mistake. Putting our items through the formulas above, and taking into account vendor costs for each of these armor upgrades as well as the helmets that go with them. Note that I'm going to use Trader Value where possible, but most items are up on the flea market at full durability for much cheaper than this as of writing.
148,092 roubles / (40 Durability / 0.5 Combined Material Multiplier) = 1851.1 Roubles per True Durability.
For this cost, you receive a class 4 helmet with effective repairs and a high ricochet chance. It protects, without further investment, the top of your head, and the back of your head down your neck.
108240 Roubles / (30 Durability / 0.45 Polymer Material Multiplier) = 1623.6 Roubles per True Durability.
For this cost, you receive class 5 protection on the top of your head, extremely effective repairs, and a high ricochet chance.
Caiman (Has no Trader Value, so we'll say 100k, which is a little higher than it is now):
100,000 Roubles / (50 Durability / 0.5 Combined Material Multiplier) = 1000 Roubles per True Durability.
Again, a class 4 helmet with effective repairs, a high ricochet chance, and the same protection areas as the FAST. It also has a mandible and visor, if you want full face protection.
73,025 Roubles / (40 Durability / 0.45 Polymer Material Multiplier) = 821 Roubles per True Durability.
The applique isn't actually up armor, but just layered armor. It actually takes less total damage than the Caiman itself by 11 points, but we'll get to why you shouldn't worry about that soon.
And Finally, the Ronin Ballistic Helmet:
146,442 Roubles / (60 durability / 0.25 Aramid) = 610.1 Roubles per True Durability.
For the cost of the Ronin, you get FULL class 3 protection of your head. You don't get an annoying visor slapped over your screen, and your vision is not restricted one bit. Disadvantage here is the high sound reduction, and the biggest problem is the low ricochet chance. As most people know now, ricochet is 90% of the time what's going to save you from a player, and at class 3 you're going to have a bad time against mid tier ammo, so what, exactly, is the Ronin for? The Ronin is the ultimate protection from every scav on the map. Anything smaller than 7.62 PS ammo will hardly scratch it. It has 240 total durability, and with the exception of the Djeta helmet and the Tank Crew helmet, will take more punishment than anything else. There is not a single body armor in the game that will take more 0 pen rounds. Would I recommend buying it? I mean probably not, most people's problems aren't stemming from being tapped by low tier scavs when they're geared out, but it's not quite as bad as everyone makes it out to be. If they simply made it high ricochet chance, it would be far and away a better investment than any of the FAST like helmets even against players as far as pure protection level goes.
So economically speaking, consider the following. If I'm spending 100k on a Caiman, am I expecting to lose it the first raid you take it out? The answer should be yes, of course, your gear is gone the second you enter the map, but we'll say that I can afford to be greedy long term and I'm banking on repeating the action enough times that I care how effective repairing my helmet is. So we're expecting that, eventually, my helmet is going to save me from a bullet. It's going to either ricochet or do full damage, but either way, it's going to be damaged. I can either replace it or repair it. We'll say I got hit by a scav using an 855 ADAR for the purposes of this. 855 does 50 base damage, but has a 37% armor damage multiplier, so it's done 19*0.5=9.5 points of damage to my helmet. Because Combined Materials is Average as far as repair goes, even if I use Mechanic to repair it, which will cost 20-30k+ roubles, I'm still going to eat average a 4 point drop from my total maximum, and at 50 total, that's basically turned my helmet into a class 3 helmet as far as penetration is concerned. (This isn't exactly how it works but it's close enough to work for the point)
So it's really not viable for me to use my Caiman still, so I sell it back for however much ragman will give me ( 80k~) leaving me 45k in the hole. (100k base cost, 25k repair cost, 80k resell gain) However, if I'd shelled out for the Applique, I could resell it for 35k. As of writing, that means I get nearly 100% of the value back off my flea market price, but we'll assume you're buying from Peacekeeper for consistency. The applique takes 19*0.45=8.5 points of damage, but has very good repair, leaving it squarely below a 1 point drop off maximum durability. This should, in theory, leave it nearly perfect condition as far as ballistic properties are concerned. I should be able to repeat the repair at least once more without needing to replace it and expect to see similar results protection wise. However, even if I DON'T see those results, I can hedge my bets, because I know that they need to beat 2 layers of RNG to actually hit my head when shooting top of head. Each layer calculates its own ricochet chance (as far as I'm aware, I'm not 100% on this being the case with pieces that cover the same area) as well as penetration. Because I'm able to repair twice, instead of having to rebuy my applique or even the Caiman itself, I can save somewhere in the realm of 100k+ roubles on my helmet over those three runs I get out of it over just rebuying.
the SLAAP plate is even better, but I'm sure you can figure out why adding class 5 to a light helmet might make it better, and other than that the same rules as the Applique still apply. Also consider the extra armor for the Bastion. Up armor from class 4 to 6, but you do have to replace it when you get hit as it's ceramic.
If you actually read this whole thing, I hope you learned something, if not, there's a few things in there I'd suggest you at least skim, so you understand what exactly you're buying with your money. Who knows, we might actually have to worry about this stuff next wipe.