Bark

Bark is a material added by Better With Mods. Bark can be made in various different ways, generally when a log is produced into planks (Similar to Sawdust), these include: Crafting planks from logs in a crafting grid with an axe, punching wooden logs, breaking tree stumps (using any tool), and cutting wood with a Saw (Better With Mods). All of these methods can be tweaked in the config file of the mod.

Bark can be used as fuel, however, it's main use is for tanning leather in a Cauldron.

Tanning efficiency
Different types of Bark are more or less efficient for tanning leather: