From Guild Wars Wiki
Sundering is a weapon upgrade that grants a 10-20% chance of having an additional 20% armor penetration added to an attack. A Sundering upgrade will not add as much damage as a Vampiric upgrade in most situations.
- Armor penetration +20% (Chance: 10...20%) or Armor penetration +10% (Chance: 5...20%)
Upgrade components which provide this bonus
- The current maximum for a Sundering upgrade is "+20% (Chance: 20%)", it used to be "+10% (Chance: 10%)".