Advancement Table Level XP Req'd Effect First 350 Add'l Dmg Resist Second 900 Add'l Dmg Resist Third 1,800 Add'l Dmg Resist Fourth 4,800 Add'l Dmg Resist Fifth 9,000 Add'l Dmg Resist Sixth 19,000 Add'l Dmg Resist Seventh 38,000 Add'l Dmg Resist

Toughness is your basic resistance to damage - your 'natural armor'. THe tougher you are, the less damage you will take from each blow.