Defense Augments

Defensive Augments are applied to armor in order to increase defense to one of the three damage types: physical, heat, or toxic. Each armor piece can have a maximum of two different augments. Defensive augments greatly magnify defense; armor without any defensive augmentation is only a fraction as effective, and for weaker armor pieces the defensive contribution without augments can be almost negligible.

Defensive augments use the following formula: Additional armor points per level = α × B + M Where:
 * α varies depending on the augment and the level
 * For Fortified and Heat Resistant: α = 0.2 for levels 1-5, then α = 0.3 starting at level 6
 * For Hazchem: α = 0.3 for levels 1-4, then α = 0.4 for levels 5 and 6, and finally α = 0.5 starting at level 7
 * B is the base armor points for the corresponding damage type (e.g. 25, 5, 0 for a Rubicon Power Assist vest for either physical, heat, or toxic)
 * M is 24 for leggings and helmets, 40 for vests and 12 for gloves and boots

Tips
Armor reduces incoming damage by a percentage. This % Damage Reduction is equal to the square root of your total defense taken from all armor pieces in that category up until a certain point. For example, 100 total physical defense is 10% reduced damage from physical attacks; 1000 total Heat defense is 32% reduced damage from heat attacks. Damage reduction changes at around 80%, requiring more defense points for higher protection. 99% is the max and is achieved with a total of 21,125. The amount defense for a category can be moused over in the armor equipment screen to see % Damage Reduction.
 * Boots and gloves are most desirable for non-defensive augmentation if the player is looking for a balanced suit of armor. This is because the same armor pieces that have greater "X" modifiers also tend to have the highest base armor. This makes vests by far the greatest contributor to defense, while most boots and gloves are arguably negligible in comparison.
 * Because the bonus defense from augmentation depends on up to 2.5x the base armor value, choosing the correct armor for defensive augmentation is critical.
 * The highest base physical defense available is from the Rubicon Hardplate Series.
 * The highest base heat defense available is from the Ronson "R" Series. Ronson is the most common brand of armor for maximizing the three defense types. (Hardplate is just barely below Ronson in terms of thermal defense, and so tanks might just go with Hardplate to get high defense in two types.)
 * The highest base toxic defense is from the Atomic Medusa Series.
 * Although melee attacks are almost always physical, the most dangerous zombies—arguably the only relevant zombies to consider when it comes to preparing a defense—are elite zombies. As elites, they are also more likely to possess a non-physical attack, meaning Heat and Toxic defense may be more important than assumed. Beware in particular elite Dark Minions whose attacks ignore 75% of armor. Besides elite zombies, you may want to build your defense to protect you from what you consider to be the deadliest threats:
 * Physical damage: Necrosis blue spawn and Devastator.
 * Heat damage: Wicker and Necrosis red spawn.
 * Toxic damage: pools of acid left over from elite zombies with Acid Blood or zombie Spitter and Regurgitator ranged attacks, Necrosis green spawn.
 * Necrosis fires projectiles with all three damage types, although the physical projectile is probably the most dangerous, as it bounces off walls, making it difficult to avoid.
 * Unless you are going for a specialized defense against a specific damage type, the augmentation "Body Fueling" provides up to a 30% increase (grade 12) in health, which may be more efficient for a general defensive set up against all damage types. This depends on how much healing you are typically able to access, as frequent healing makes extra health less useful.
 * Heavy class players who max Tough Body may benefit more from bonus health, as % Damage Reduction between Tough Body and armor stacks multiplicatively.
 * Body Fueling and Toughness (the bonus health skill) have no unique synergistic implications, as Body Fueling is multiplicative, always affecting survivability by the same proportion regardless of how many points are placed into Toughness.
 * The skill Body Armour Expert multiplies armor value by 7% per point. For high armor builds, especially ones prioritizing defensive augments, Body Armour Expert can be the most efficient way to maximize defense; but remember: Dark Minions ignore 75% of armor.

Trivia

 * A single Black Hardplate Chest, Ronson Vest, and Medusa Vest with 12 Fortified, 12 Heat Resistant, and 12 Hazchem, respectively, along with 25 points in the Body Armour Expert skill can achieve 99% damage reduction for their respective categories. (Hardplate can also achieve 99% thermal damage reduction through this method.)
 * Highest possible defenses (with 25 Body Armor Expert and all collections and masteries):
 * The highest total Physical defense possible is 112,801.4 with full Black max cored Hardplate.
 * The highest total Heat defense possible is 75,534.3 with full Black max cored Ronson helmet & vest and Hardplate gloves, pants, & boots.
 * The highest total Toxic defense possible is 132,851 with full Black max cored Medusa.