Armour and Energy Shield Mastery is a passive skill.
(New) 2% chance per 5% missing Energy Shield to Defend with 150% of Armour
(New) Recover 5% of Energy Shield over 1 second when you take Physical Damage from an Enemy Hit
(New) 10% of Armour also applies to Chaos Damage taken from Hits
Increases and Reductions to Armour also apply to Energy Shield Recharge Rate at 20% of their value
(New) 100% increased Armour and Energy Shield from Equipped Body Armour if Equipped Gloves, Helmet and Boots all have Armour and Energy Shield
(New) 10% of Physical Damage from Hits taken as Chaos Damage
Here you can see the Armour/Energy Shield mastery has more options available than before. The other thing we focused on with this one is tying the mechanics together better.
Instead of some being about armor and some being about energy shield, we've tried to make sure each really emphasizes having both armor and energy shield.