Star Wars Knights of the Old Republic II: The Sith Lords/Upgrade items, armor

All overlays and underlays can be created using a workbench with sufficient skill rank and components, although when armor, overlay and underlay grant the same bonuses, these don't always combine as expected or displayed in the upgraded armor's description.

Only the highest attribute bonus is actually granted, so upgrading a (: +2) with a  Mark V (Strength: +3) only grants Strength: +3, not +5, according to both its description and the  screen (among other things). However, penalties behave as expected (although descriptions don't always correctly display the following):

bonuses actually sum as expected, but only the highest bonus is granted. For example:

The description for this upgraded armor only displays the highest bonus for both, but after failure to save against a (and with no other damage reduction), its fire damage is reduced from 36 to 3 (36 - 36*0.5 - 15), not the expected 0 (36 - 36*0.5 - 15 - 10 - 10) or, based on the description, 11 (36 - 36*0.3 - 15), indicating a 50% reduction, not just 30%.

Overlays
Alloy overlays can enhance armor performance. The modifications require a workbench with adequate tools and armor of high quality marked as upgradeable.

Heat Shielding
Special: Upgrade Item, Armor

Armorply Plating
Special: Upgrade Item, Armor

Armorply Plating Mark II is the only overlay which can upgrade the, and other upgradeable robes.

Sound Dampening Overlay
Special: Upgrade Item, Armor

Energy Shielding
Special: Upgrade Item, Armor

Ballistic Shielding
Special: Upgrade Item, Armor

Ablative Plating
Special: Upgrade Item, Medium or Heavy Armor

Bonded Plates
Special: Upgrade Item, Medium or Heavy Armor

Heavy Bonded Plates
Special: Upgrade Item, Heavy Armor

Underlays
Underlay can have a variety of effects on the armor to which it is applied. The modifications require a workbench with adequate tools and armor of high quality marked as upgradeable.

Environment Underlay
Special: Upgrade Item, Armor and ../Robes/

Biorestorative Underlay
Special: Upgrade Item, Armor and ../Robes/

Armorweave Underlay
Special: Upgrade Item, Armor

Strengthening Underlay
Special: Upgrade Item, Armor

Durasteel Underlay
Special: Upgrade Item, Armor

Flexible Underlay
Special: Upgrade Item, Heavy Armor