Shadow Armor

Shadow armor is the best body armor for thieves and it's sold at the Thunderhammer Smithy for a hefty sum of gold. It's studded leather armor specially made for the Shadowmasters of Amn, the highest order within the Shadow Thief hiearchy.

In-game description
"Shadow armor is studded leather armor created for use by the Shadowmasters of Amn. The Shadowmasters are of the highest order within the Shadow Thief hiearchy. It is +3 studded leather armor that melds into shadows."