Untwisting Iron Skin (Combat)Source Inner Sea Combat pg. 13 (Amazon)
Your training has tempered your flesh to resist blows as though it were forged iron.
Prerequisites: Str 15, Wis 13, Perfect Style, Toughness, Untwisting Iron Strength, base attack bonus +13 or monk level 13th.
Benefit: When using Perfect Style, you gain an amount of DR/adamantine equal to 1/3 your character level (maximum 6). Additionally, whenever you break an item with at least hardness 10, you gain DR 1/— for a number of rounds equal to half the item’s hit points (maximum 10 rounds); the value of this damage reduction increases by 1 for every 5 points of hardness above 10 the broken item possessed. You can spend 1 ki point as a swift action to double either of the damage reduction values granted by this feat for 1 round.Source Weapon Master's Handbook pg. 25 (Amazon)
You can spend 2 stamina points instead of 1 ki point when using Untwisting Iron Skin.