Variation of Armor that's difficult to detect and absorbs some damage that penetrates DR. It lasts until it has absorbed it's maximum damage.

Invisible Armor [33] 
    Damage Resistance 1 [12.5] 
        Force Field [+20%] 
    Vitality Reserve 5 [20] 
        See GURPS FAQ 5.1.5 
        Doesn't Heal [-30%] 
    No Signature [+20%] 
    Extended Duration (Permanent) [+150%] 
        Lasts until the Vitality Reserve is used up 
    Magical [-10%] 
    Spell Components [-30%] 
        Must say "armor" in Latin 
        Must gesture with hands 
        Must hold a piece of plate mail 
Level 2 [45] 
    Add 1 to DR [12] 
Levels 3+ [+12.5/level] 
    Add 1 to DR [+5 base] 
Reserve Levels 1+ [+4/level] 
    Increase Vitality Reserve by 1 level [+2 base]