A bag used by professional thieves and ninjas. Well made and designed not to hinder your stealth while you fill it with other people's possessions.

–In-game description

The thieves backpack is a medium backpack that reduces encumbrance by 60% and does not hinder your stealth. It slightly hinders combat abilities but less than some other backpacks.

It can be purchased from General Item Trader at World's End settlement for 5000 cats.