The Armiger series of feats are meant to be individually worthwhile as good (but not game-breaker) feats, but each is slightly less useful than the previous. Taking all three results in a very specialised character. Battle Rush is my take on the fighter who can carry on "forever" while in melee.
Armiger
You know how to use your armour to mitigate damage.
Prerequisite: Base attack bonus +4
Benefit: Your armour provides damage resistance against piercing, slashing, and bludgeoning damage, up to a limit of your BAB or half (your armour's armour bonus (plus enhancement bonus, if any)), whichever is lower.
Normal: Your armour provides it's armour bonus to AC as normal, but it does not provide any damage resistance.
Improved Armiger
You know how to use your armour to mitigate damage.
Prerequisite: Base attack bonus +9, Armiger
Benefit: Your armour provides damage resistance against piercing, slashing, and bludgeoning damage, up to a limit of your BAB or your armour's armour bonus (plus enhancement bonus, if any), whichever is lower.
Greater Armiger
You know how to use your armour to mitigate damage.
Prerequisite: Base attack bonus +16, Armiger, Improved Armiger
Benefit: Your armour provides damage resistance against piercing, slashing, and bludgeoning damage, up to a limit of your BAB or two times (your armour's armour bonus (plus enhancement bonus, if any)), whichever is lower.
Battle Rush
Prerequisites: Base attack bonus +3, Constitution 13
Benefit: A number of times per day equal to your Constitution bonus, you an enter a battle rush. This rush lasts for ten minutes. While in a battle rush, half of any damage you inflict on an enemy in melee gets returned to you as temporary hit points. These temporary hit points are lost first when you take damage, and automatically vanish at the end of the battle rush period.
Note: For the purposes of this feat, an enemy is only counted if they are aware of your presence, and have a chance of causing hit point damage to you in that round. It does not count if you hypothetically leave yourself open to attack (only your actual actions that round count), but it does count if they can do so in a way that puts them at greater risk than might otherwise be considered safe.
On review, Battle Rush is horribly overpowered.
The Armiger feats have been de-powered from x1/2/3 to x0.5/1/2 armour bonus, to prevent so much front-loading.
"Damage resistance" is my house rule term which takes the energy resistance and expands it to cover physical damage types in addition to energy damage types.