Standard armor is worth 30 points per ton. As standard armor is carried on the outside of the 'Mech it takes no slots. The maximum armor a location can carry is twice its internal structure value. A 'Mech's torso locations have separate armor for front and rear and the sum of their armor point values must comply with the "twice internal structure" rule.
- Endo-Steel Structure
- The standard internal structure of a 'Mech weighs 10% of its maximum tonnage. If replaced with endo-steel a 'Mech's internal structure weighs only 5% of its maximum tonnage. While lighter, endo-steel is more bulky than standard structure - Inner Sphere (IS) endo-steel takes 14 slots and Clan endo-steel takes 7 slots. These occupied structure slots are not dedicated to specific locations.
- Ferro-Fibrous Armor
- Provides 12% more armor per ton but is more bulky than standard armor - IS ferro-fibrous takes 14 slots and Clan ferro-fibrous takes 7 slots. These occupied armor slots are not dedicated to specific locations.
- Light Ferro-Fibrous Armor
- IS only. Like ferro-fibrous, but only provides 6% more armor per ton. Takes 7 slots, and these occupied armor slots are not dedicated to specific locations.
- Stealth Armor
- IS only. Removes 'Mech from enemy heat vision and sensors, even from UAVs. When active the 'Mech does not dissipate heat. When powered off stealth cannot be re-enabled for 10 seconds. Takes 10 slots, two slots each in the right arm, left arm, right side torso, left side torso, right leg and left leg.
- Cellular Ammunition Storage Equipment (CASE)
- Upgrades location structure to block ammunition explosion damage from transferring to other locations. The full damage will still occur within the original location. For example, adding CASE to the side torso when using an IS XL engine will not save the 'Mech from destruction if there is an ammunition explosion within the side torso. Clan 'Mechs get CASE automatically, whereas IS 'Mechs must mount CASE to each location. IS CASE takes a slot but has no tonnage.
If a gauss rifle or non-gauss ammunition bin is destroyed there is a chance for them to explode, causing additional damage to the 'Mech. Internal explosions bypass neighboring location armor with respect to damage transfer.
An ammunition bin has a 10% chance to explode when destroyed, dealing damage as a single hit to its location. The damage depends on the amount of ammunition remaining in the bin. The ammunition within a destroyed bin is lost, whether or not it explodes.
IS gauss rifles have a 90% chance to explode when destroyed and Clan gauss rifles have a 100% chance to explode when destroyed - dealing damage as a single hit to its location. The amount of damage an explosion deals depends on the type of gauss rifle.
As stated in Heat, excessive 'Mech heat will cause internal damage to a randomly selected location. Like ammunition and gauss rifle explosions, heat damage bypasses location armor with respect to damage transfer.