Vests are protective equipment that reduces damage or increases elemental resistance. Vests can be crafted or upgraded at tanning racks, using hides from deer, bears, snakes, or bison. Skinning these animals either gives normal or superior pelts/hides, the latter of which is needed to upgrade vests to higher rarities. The trader at Fort Glenn has a high chance to have a legendary vest on sale, together with a legendary bow.
Stoneskin Vest, an end-game armor that appears to be made from Cave Terror hides, can be found in Old Ginkgo Temple during the Oneirist Journey. Constance Driftwood needs to interact with the stele in Blood Moon temple in order to reveal the location of the Old Ginkgo temple.