Armor damage reduction in Remnant works very similarly to that of many other games, like League Of Legends for example.
The basic formula to determine how much less damage players take in percent is as follows:
%dmg reduction: 100 / (100 + armor value)
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This function is of hyperbolic shape, which could lead players to believe that there are diminishing returns in terms of survivability gain, but that is shown to be untrue if converted to effective HP (eHP) gained:
To determine how many points of damage a player could actually sustain without dying, we would need to convert the %damage reduction from armor into a function that also factors in the player's nominal HP.
The easiest way to visualize how armor affects the player's survivability is thinking of each point of armor increasing effective HP by 1%
Without any changes to players' starting health of 100 HP, the resulting formula would look very simple:
eHP (@100 HP) = 100 + armor value
at 100 armor, the player would be able to sustain 200 points of damage before dying, at 350 armor, they would have 450 eHP and so on.
factoring in players' variable nominal HP, the most coherent way to structure the formula would be:
eHP = (nominal Health / 100) x (100 + armor value)
where nominal Health / 100 is merely the ratio of HP the player has more or less than the base of 100 HP
<aside> 💡 Example: 150 nominal HP (with maxed Vigor Trait) & 350 armor → eHP = (150/100) x (100 + 350) → 1.5 x 450 = 675 eHP
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Conclusion: Neither HP nor armor increases suffer diminishing returns to survivability.