Warbear Leather comes from the hides of extremely powerful bears. The bear's skin has toughened to protect them from extremely tough conditions.
Sources
This item is created by skinning bears that level 50 and higher. These bears can include Shardtooth Bears in Winterspring and Tainted Black Bears in Blasted Lands.
As an ingredient
Leatherworking
Patch changes
Patch 6.0.2 (2014-10-14): Stacks to 200, up from 20.
Patch 1.12.0 (2006-08-22): Now stacks to 20.