Toughness is a Defence stat that reduces the amount of damage taken from Skillz based attacks. The higher your Toughness, The more damage that is removed. If it's high enough you can block off all damage taken.
Toughness Upgrades:
Plastic Armor: +20 to Toughness. Costs 300 Tix.
Metal Armor: +35 to Toughness. Costs 460 Tix.
Plate Armor: +55 to Toughness. +200 to Health. Costs 300 Tix + Plastic Armor + Metal Armor + Mesh Character.
Armored Shoes: +2 to Speed, +8 to Toughness. Costs 240 Tix + Shoes.