Minecraft wiki entry for Protection, associated text: The protection enchantment is applied after the armor's damage reduction. For example, 20 armor points provide a 4% * 20 = 80% damage reduction. If the total protection enchantment levels on said armor adds up to 10, they would provide 40% damage reduction. This would equate to a result of 88% damage reduction, as it stacks multiplicatively rather than additively (80% + 40% * (100% - 80%), rather than 80% + 40%).