Leather Armor +1

Leather Armor +1 is improved leather armor. It's sold at the Thunderhammer Smithy and can be obtained as loot in the area with tombs east of Nashkel when fighting a group of assassins.

In-game description
"Leather armor, despite the popular misconception, is not soft and supple like the leather used to make a ranger's boots or a druid's robe.  That kind of leather offers no better protection than common clothing."