Pannier Panniers will increase a dwarves inventory capactiy by 4. Since they take up one space you will really only gain 3 spaces. When you are using a Pannier to carry more than 6 items your dwarf will walk slow and be visibly be wearing the pannier as a backpack.

Panniers are produced at a Log

Invention: 6 Wood, 6 Transport

Production: FungusStemx1