The highest armour value you are wearing applies, that much is clear from the rulebook. So you can't combine a Armor jacket and vest for some 20 armor points.
But say that I wanted to stack an effect from some armour, such as a ghillie suit from run and gun, but keep my armour jacket under it so I won't die from someone looking at me meanly? Wouldn't this still make the character concealable and armoured? How much would these two weigh together, as in, should I receive penalties from encumbrance?